Add the port "fixed_ips" information in the DHCP RPC

In [1], a method to process the DHCP events in the correct order was
implemented. That method checks the port events in order to match
the "fixed_ips" field. That implies the Neutron server provides this
information in the port event, sent via RPC.

However in [2], the "fixed_ips" information was removed from the
``DhcpAgentNotifyAPI._after_router_interface_deleted``, causing a
periodic error in the ``DHCPResourceUpdate.__lt__`` method, as reported
in the LP bug. This patch is restoring this field in the RPC message.

[1]https://review.opendev.org/c/openstack/neutron/+/773160
[2]https://review.opendev.org/c/openstack/neutron/+/639814

Closes-Bug: #2071426
Change-Id: If1362b9b91794e74e8cf6bb233e661fba9fb3b26
(cherry picked from commit b0081ac6c0)

neutron/api/rpc/agentnotifiers/dhcp_rpc_agent_api.py

@@ -284,6 +284,7 @@ class DhcpAgentNotifyAPI(object):
         port = payload.metadata.get('port')
         self._notify_agents(payload.context, 'port_delete_end',
                             {'port_id': port['id'],
+                             'fixed_ips': port['fixed_ips'],
                              'network_id': port['network_id']},
                             port['network_id'])
 

neutron/tests/unit/api/rpc/agentnotifiers/test_dhcp_rpc_agent_api.py

@@ -251,6 +251,7 @@ class TestDhcpAgentNotifyAPI(base.BaseTestCase):
         payload = events.DBEventPayload(
             mock.Mock(), metadata={
                 'port': {'id': 'foo_port_id',
+                         'fixed_ips': mock.ANY,
                          'network_id': 'foo_network_id'}})
         self._test__notify_agents_with_function(
             lambda: self.notifier._after_router_interface_deleted(