Bug 1844 : Callback from neutron's router interface to be handled via neutron port events

In the absence of explicit router interface add/remove callback, check the interface
owner of the neutron port and determine if that represents a router interface. From there,
simply map the event as the expected router interface event.

Change-Id: Ib5a58ad166e632b89cc97a23b2c8545f6462ca66
Signed-off-by: Flavio Fernandes <ffernand@redhat.com>