AVX-50899: fqdn_lan_interface is not needed for firenet fqdn association

[shanxu2017]

Issue

After create Firenet FQDN association, reapply same config, will cause destroy and reapply due to fqdn_lan_interface change

aviatrix_firewall_instance_association.arm_fqdn_gw_association[0] must be replaced
-/+ resource "aviatrix_firewall_instance_association" "arm_fqdn_gw_association" {
      ~ id              = "arm-transit-firenet-vnet:rg-av-arm-transit-firenet-vnet-817240:228a1824-5210-4398-97bb-f7bf5900da65~~arm-transit-firenet-gateway~~arm-fqdn-transit-firenet-gw" -> (known after apply)
      ~ lan_interface   = "av-nic-arm-fqdn-transit-firenet-gw_eth-fqdnlan0" -> "av-nic-arm-fqdn-transit-firenet-gw_eth1" # forces replacement
        # (5 unchanged attributes hidden)
    }

RCA

av-nic-arm-fqdn-transit-firenet-gw_eth1 is from avixtrix_gateway resource, however, this value is hard-coded in terraform code, not from controller API response.
av-nic-arm-fqdn-transit-firenet-gw_eth-fqdnlan0 is from Firenet resouce, which is returned from controller API response.
These 2 values mismatch.

Fix

For Firenet FQDN gateway, this fqdn_lan_interface is not used at all. Controller/copilot UI doesn't use it as well. Only controller backend use it internally.
Therefore, set it to empty value and remove from terraform logic.

[inc1t3Ful]

By removing the fqdn_lan_interface from outputting in the gateway resource/data source, there is no way to pass a lan_interface into the aviatrix_firewall_instance_association resource. Is that intended to be unnecessary now as an input for attaching the FQDN gateway to Firenet?

[shanxu2017]

By removing the fqdn_lan_interface from outputting in the gateway resource/data source, there is no way to pass a lan_interface into the aviatrix_firewall_instance_association resource. Is that intended to be unnecessary now as an input for attaching the FQDN gateway to Firenet?

You can pass lan_interface into the aviatrix_firewall_instance_association resource. I didn't remove it. I tested, pass in no problem. The code just ignore whatever passed in.

[inc1t3Ful]

LGTM