Comment 0 for bug 1763656

RHEL 7.5 has kernel version updated to 3.10.0-862.el7, which breaks building of vrouter module.

```
  CC [M] /home/zuul/contrail-5.1.0/vrouter/linux/vhost_dev.o
/home/zuul/contrail-5.1.0/vrouter/linux/vhost_dev.c: In function 'vhost_setup':
/home/zuul/contrail-5.1.0/vrouter/linux/vhost_dev.c:466:8: error: 'struct net_device' has no member named 'max_mtu'
     dev->max_mtu = ETH_MAX_MTU;
        ^
```

Afterwards:
```
  CC [M] /home/zuul/contrail-5.1.0/vrouter/linux/vr_host_interface.o
/home/zuul/contrail-5.1.0/vrouter/linux/vr_host_interface.c: In function 'linux_if_tx_csum_offload':
/home/zuul/contrail-5.1.0/vrouter/linux/vr_host_interface.c:1711:17: warning: unused variable 'driver_name' [-Wunused-variable]
     const char *driver_name;
                 ^
  CC [M] /home/zuul/contrail-5.1.0/vrouter/linux/vr_genetlink.o
/home/zuul/contrail-5.1.0/vrouter/linux/vr_genetlink.c:37:21: error: 'GENL_ID_GENERATE' undeclared here (not in a function)
     .id = GENL_ID_GENERATE,
                     ^
/home/zuul/contrail-5.1.0/vrouter/linux/vr_genetlink.c: In function 'vr_genetlink_init':
/home/zuul/contrail-5.1.0/vrouter/linux/vr_genetlink.c:224:5: error: implicit declaration of function 'genl_register_family_with_ops_groups' [-Werror=implicit-function-declaration]
     return genl_register_family_with_ops_groups(&vrouter_genl_family,
     ^
cc1: some warnings being treated as errors
```