MTU too large error presented on create but not update

If an MTU is supplied when creating a network it is rejected if it is above global_physnet_mtu. If an MTU is supplied when updating a network it is not rejected even if the value is too large. When global_physnet_mtu is 1500 I can easily set MTU 9000 or even beyond through update. This is not valid.

~~~
w(overcloud) [stack@undercloud-0 ~]$ openstack network show private1
+---------------------------+----------------------------------------------------------------------------+
| Field | Value |
+---------------------------+----------------------------------------------------------------------------+
| admin_state_up | UP |
| availability_zone_hints | |
| availability_zones | nova |
| created_at | 2020-03-09T15:55:38Z |
| description | |
| dns_domain | None |
| id | bffac18a-ceaa-4eeb-9a19-800de150def5 |
| ipv4_address_scope | None |
| ipv6_address_scope | None |
| is_default | False |
| is_vlan_transparent | None |
| mtu | 1500 |
| name | private1 |
| port_security_enabled | True |
| project_id | d69c1c6601c741deaa205fa1a7e9c632 |
| provider:network_type | vlan |
| provider:physical_network | tenant |
| provider:segmentation_id | 106 |
| qos_policy_id | None |
| revision_number | 8 |
| router:external | External |
| segments | None |
| shared | True |
| status | ACTIVE |
| subnets | 51fc6508-313f-41c4-839c-bcbe2fa8795d, 7b6fcbe1-b064-4660-b04a-e433ab18ba73 |
| tags | |
| updated_at | 2020-03-09T15:56:41Z |
+---------------------------+----------------------------------------------------------------------------+
(overcloud) [stack@undercloud-0 ~]$ openstack network set private1 --mtu 9000
(overcloud) [stack@undercloud-0 ~]$ openstack network set private1 --mtu 9500
(overcloud) [stack@undercloud-0 ~]$ openstack network show private1

+---------------------------+----------------------------------------------------------------------------+
| Field | Value |
+---------------------------+----------------------------------------------------------------------------+
| admin_state_up | UP |
| availability_zone_hints | |
| availability_zones | nova |
| created_at | 2020-03-09T15:55:38Z |
| description | |
| dns_domain | None |
| id | bffac18a-ceaa-4eeb-9a19-800de150def5 |
| ipv4_address_scope | None |
| ipv6_address_scope | None |
| is_default | False |
| is_vlan_transparent | None |
| mtu | 9500 |
| name | private1 |
| port_security_enabled | True |
| project_id | d69c1c6601c741deaa205fa1a7e9c632 |
| provider:network_type | vlan |
| provider:physical_network | tenant |
| provider:segmentation_id | 106 |
| qos_policy_id | None |
| revision_number | 12 |
| router:external | External |
| segments | None |
| shared | True |
| status | ACTIVE |
| subnets | 51fc6508-313f-41c4-839c-bcbe2fa8795d, 7b6fcbe1-b064-4660-b04a-e433ab18ba73 |
| tags | |
| updated_at | 2020-03-10T15:16:15Z |
+---------------------------+----------------------------------------------------------------------------+
~~~

Here we demonstrate that while network set works, network create does not. Network create seems to have the correct behavior.

--------------------

~~~
overcloud) [stack@undercloud-0 ~]$ openstack network create --mtu 1500 --provider-physical-network tenant --provider-network-type vlan --provider-segment 109 private10
+---------------------------+--------------------------------------+
| Field | Value |
+---------------------------+--------------------------------------+
| admin_state_up | UP |
| availability_zone_hints | |
| availability_zones | |
| created_at | 2020-03-10T15:20:15Z |
| description | |
| dns_domain | None |
| id | f8b6efda-3c77-4ac0-a4dd-13773cf3f542 |
| ipv4_address_scope | None |
| ipv6_address_scope | None |
| is_default | False |
| is_vlan_transparent | None |
| mtu | 1500 |
| name | private10 |
| port_security_enabled | True |
| project_id | d69c1c6601c741deaa205fa1a7e9c632 |
| provider:network_type | vlan |
| provider:physical_network | tenant |
| provider:segmentation_id | 109 |
| qos_policy_id | None |
| revision_number | 3 |
| router:external | Internal |
| segments | None |
| shared | False |
| status | ACTIVE |
| subnets | |
| tags | |
| updated_at | 2020-03-10T15:20:15Z |
+---------------------------+--------------------------------------+
(overcloud) [stack@undercloud-0 ~]$ openstack network delete private10
~~~

~~~
(overcloud) [stack@undercloud-0 ~]$ openstack network create --mtu 2500 --provider-physical-network tenant --provider-network-type vlan --provider-segment 109 private10
Error while executing command: BadRequestException: Unknown error, {"NeutronError": {"message": "Invalid input for operation: Requested MTU is too big, maximum is 1500.", "type": "InvalidInput", "detail": ""}}
~~~

~~~
(overcloud) [stack@undercloud-0 ~]$ openstack network create --mtu 1500 --provider-physical-network tenant --provider-network-type vlan --provider-segment 109 private10
+---------------------------+--------------------------------------+
| Field | Value |
+---------------------------+--------------------------------------+
| admin_state_up | UP |
| availability_zone_hints | |
| availability_zones | |
| created_at | 2020-03-10T15:20:50Z |
| description | |
| dns_domain | None |
| id | fb8e96b4-b770-4493-a6ee-3cdae5dbf714 |
| ipv4_address_scope | None |
| ipv6_address_scope | None |
| is_default | False |
| is_vlan_transparent | None |
| mtu | 1500 |
| name | private10 |
| port_security_enabled | True |
| project_id | d69c1c6601c741deaa205fa1a7e9c632 |
| provider:network_type | vlan |
| provider:physical_network | tenant |
| provider:segmentation_id | 109 |
| qos_policy_id | None |
| revision_number | 3 |
| router:external | Internal |
| segments | None |
| shared | False |
| status | ACTIVE |
| subnets | |
| tags | |
| updated_at | 2020-03-10T15:20:50Z |
+---------------------------+--------------------------------------+
(overcloud) [stack@undercloud-0 ~]$ openstack network set private10 --mtu 2500
(overcloud) [stack@undercloud-0 ~]$ openstack network show private10
+---------------------------+--------------------------------------+
| Field | Value |
+---------------------------+--------------------------------------+
| admin_state_up | UP |
| availability_zone_hints | |
| availability_zones | |
| created_at | 2020-03-10T15:20:50Z |
| description | |
| dns_domain | None |
| id | fb8e96b4-b770-4493-a6ee-3cdae5dbf714 |
| ipv4_address_scope | None |
| ipv6_address_scope | None |
| is_default | None |
| is_vlan_transparent | None |
| mtu | 2500 |
| name | private10 |
| port_security_enabled | True |
| project_id | d69c1c6601c741deaa205fa1a7e9c632 |
| provider:network_type | vlan |
| provider:physical_network | tenant |
| provider:segmentation_id | 109 |
| qos_policy_id | None |
| revision_number | 5 |
| router:external | Internal |
| segments | None |
| shared | False |
| status | ACTIVE |
| subnets | |
| tags | |
| updated_at | 2020-03-10T15:21:08Z |
+---------------------------+--------------------------------------+