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
b0081ac6c0