Move ha router functionality from the agent to ha_router

Move ha router functionality from the agent to ha_router

This was pretty much a mechanical change.  Most of the methods passed
in ri as the first argument and so changing the way they're called was
a simple matter of replacing self with ri.  In the methods themselves,
I first made sure that self was not referenced for anything that
wasn't available in the router context and then replaced ri with self.

Change-Id: I2f9e23543a10da256d33c4c32a50aa2b8c93989d
Partially-Implements: bp/restructure-l3-agent