Add the verify of network_id in _test_create_interface_by_port_id

When create interface by port_id,
not only iface['port_id'] is equal to port_id,
but also iface['net_id'] should be same with network_id.

I think only check iface['port_id'] is not enough.

Change-Id: I82b53a996e8a3c1945fd16a7cf10ee85850be60d
diff --git a/tempest/api/compute/servers/test_attach_interfaces.py b/tempest/api/compute/servers/test_attach_interfaces.py
index 0248c65..3c057ac 100644
--- a/tempest/api/compute/servers/test_attach_interfaces.py
+++ b/tempest/api/compute/servers/test_attach_interfaces.py
@@ -123,7 +123,7 @@
             server['id'], port_id=port_id)['interfaceAttachment']
         iface = waiters.wait_for_interface_status(
             self.interfaces_client, server['id'], iface['port_id'], 'ACTIVE')
-        self._check_interface(iface, port_id=port_id)
+        self._check_interface(iface, port_id=port_id, network_id=network_id)
         return iface
 
     def _test_create_interface_by_fixed_ips(self, server, ifs):