[VNC OpenStack] Filter port list with network back-ref

On port list, when the filter network IDs is provided we can filter VMIs
with back reference to that network IDs.

Closes_bug: #1646137

Change-Id: I5c479e6f4b3e512d1b24a6b415f4fa0633d5d2ba

src/config/vnc_openstack/vnc_openstack/neutron_plugin_db.py

@@ -3786,6 +3786,8 @@ def port_list(self, context=None, filters=None):
                     except NoIdError:
                         continue
                     ret_q_ports.append(port_info)
+            elif 'network_id' in filters:
+                ret_q_ports = self._port_list_network(filters['network_id'])
             else:
                 ret_q_ports = self._port_list_project(project_id,
                                                   is_admin=context['is_admin'])