[L3] Delete DvrFipGatewayPortAgentBindings after no gw ports

This is the code behavior aligning for dvr related logical. The
L3 dvr DB will remove all related FIP agent gateway port after there
is no real use of it. But the DvrFipGatewayPortAgentBindings remain,
it will cause the issue of new floating IP failed to bind. This
patch adds the binding deleting action.

Related-bug: #1883089
Change-Id: I62c29e172bc8705dade11d37bb347241ef8ad5f8

neutron/db/l3_dvr_db.py

@@ -371,6 +371,11 @@ class DVRResourceOperationHandler(object):
             # to clean up the fip namespace as it is no longer required.
             self.l3plugin.l3_rpc_notifier.delete_fipnamespace_for_ext_net(
                 payload.context, network_id)
+            # Delete the Floating IP agent gateway port
+            # bindings on all hosts
+            l3_obj.DvrFipGatewayPortAgentBinding.delete_objects(
+                payload.context,
+                network_id=network_id)
 
     def _delete_fip_agent_port(self, context, network_id, host_id):
         try:

neutron/tests/unit/db/test_l3_dvr_db.py

@@ -1344,3 +1344,27 @@ class L3DvrTestCase(test_db_base_plugin_v2.NeutronDbPluginV2TestCase):
             self.assertRaises(
                 exceptions.BadRequest,
                 self.mixin._get_assoc_data, self.ctx, mock.ANY, mock.Mock())
+
+    def test__delete_dvr_internal_ports(self):
+        payload = mock.Mock()
+        payload.context = mock.Mock()
+        payload.latest_state = {'distributed': True}
+        payload.metadata = {'new_network_id': 'fake-net-1',
+                            'network_id': 'fake-net-2'}
+        plugin = mock.Mock()
+        directory.add_plugin(plugin_constants.CORE, plugin)
+        plugin.get_ports.return_value = []
+        with mock.patch.object(self.mixin,
+                               'delete_floatingip_agent_gateway_port') as \
+            del_port, \
+            mock.patch.object(
+                self.mixin.l3_rpc_notifier,
+                'delete_fipnamespace_for_ext_net') as \
+            del_fip_ns, \
+            mock.patch.object(router_obj.DvrFipGatewayPortAgentBinding,
+                              "delete_objects") as del_binding:
+            self.mixin._delete_dvr_internal_ports(
+                None, None, resources.ROUTER_GATEWAY, payload)
+            del_port.assert_called_once()
+            del_fip_ns.assert_called_once()
+            del_binding.assert_called_once()