RPC additions to support DVR

This patch introduces the RPC contract changes
required for both the server (plugin) and agent
to propagate and retrieve additional information
about Distributed Routers, like MAC addresses
and Port Bindings.

Partially-implements: blueprint neutron-ovs-dvr

Change-Id: I04a2ee5fceea79d2786c799178f8dd1675925a39
Authored-by: Vivekanandan Narasimhan <vivekanandan.narasimhan@hp.com>
Co-Authored-By: Armando Migliaccio <armamig@gmail.com>
Merge "RPC additions to support DVR"