maas 3.1 creates alias when editing vlan instead of saving changes

Hi there, could you please provide the output of `maas $PROFILE interfaces $SYSTEM_ID` of the machine with the original config, and the same command's output for the machine with the alias issue? Additionally, how are you cloning said config?

to be clear, this happens with all my systems, not just one. the bug seems universal. I'm using the "Clone from..." feature in the GUI to clone the systems storage and networking. here's the output from one of the affected systems:

```
# maas admin interfaces read 4smwte
Success.
Machine-readable output follows:
[
    {
        "parents": [],
        "sriov_max_vf": 128,
        "tags": [
            "sriov"
        ],
        "effective_mtu": 9000,
        "type": "physical",
        "link_connected": true,
        "name": "ens5f0",
        "enabled": true,
        "vlan": {
            "vid": 0,
            "mtu": 9000,
            "dhcp_on": true,
            "external_dhcp": null,
            "relay_vlan": null,
            "id": 5004,
            "primary_rack": "apcxt8",
            "secondary_rack": null,
            "name": "untagged",
            "fabric": "tr2_int",
            "space": "undefined",
            "fabric_id": 2,
            "resource_uri": "/MAAS/api/2.0/vlans/5004/"
        },
        "id": 50,
        "system_id": "4smwte",
        "mac_address": "b4:96:91:b9:0a:f8",
        "children": [
            "int"
        ],
        "firmware_version": "2.25 0x80007029 0.0.0",
        "params": {},
        "link_speed": 10000,
        "interface_speed": 10000,
        "vendor": "Intel Corporation",
        "product": null,
        "links": [],
        "numa_node": 0,
        "discovered": null,
        "resource_uri": "/MAAS/api/2.0/nodes/4smwte/interfaces/50/"
    },
    {
        "parents": [],
        "sriov_max_vf": 128,
        "tags": [
            "sriov"
        ],
        "effective_mtu": 9000,
        "type": "physical",
        "link_connected": true,
        "name": "ens5f1",
        "enabled": true,
        "vlan": {
            "vid": 0,
            "mtu": 9000,
            "dhcp_on": true,
            "external_dhcp": null,
            "relay_vlan": null,
            "id": 5004,
            "primary_rack": "apcxt8",
            "secondary_rack": null,
            "name": "untagged",
            "fabric": "tr2_int",
            "space": "undefined",
            "fabric_id": 2,
            "resource_uri": "/MAAS/api/2.0/vlans/5004/"
        },
        "id": 51,
        "system_id": "4smwte",
        "mac_address": "b4:96:91:b9:0a:f9",
        "children": [
            "int"
        ],
        "firmware_version": "2.25 0x80007029 0.0.0",
        "params": {},
        "link_speed": 10000,
        "interface_speed": 10000,
        "vendor": "Intel Corporation",
        "product": null,
        "links": [],
        "numa_node": 0,
        "discovered": [],
        "resource_uri": "/MAAS/api/2.0/nodes/4smwte/interfaces/51/"
    },
    {
        "parents": [
            "ens5f0",
            "ens5f1"
        ],
        "sriov_max_vf": 0,
        "tags": [],
        "effective_mtu": 9000,
        "type": "bond",
        "link_connected": false,
        "name": "int",
        "enabled": true,
        "vlan": {
            "vid": 0,
            "mtu": 9000,
            "dhcp_on": true,
            "external_dhcp": null,
            "relay_vlan": null,
            "id": 5004,
            "primary_rack": "apcxt8",
      ...

This seems to be a UI bug. When calling update_interface, "link_id" should be passed with the ID of the current StaticIPAddress. If that's not provided, MAAS interprets the request as adding a new IP to the interface (causing an alias to be added).