We can't detect error if in network template used add-port on non existent NIC

[Alexander Kislitsky]

It is impossible to check that NIC is not existed if in the network template used add-port on tagged interface on non existent NIC:

{
  "action": "add-port",
  "bridge": "br1",
  "ethtool": {
    "offload": {
      "large-receive-offload": false,
      "generic-receive-offload": false
    }
  },
  "name": "fake.222",
  "mtu": 9000
},

Actual:
template is uploaded successfully

Expected:
error is raised