Addressed comments from ietf list…

- Inter-domain (AS) specific stuff is out from the main grammar. I've
added a new section called "Inter-domain extensions to the RIB" that
puts back all the inter-domain stuff as optional augmentations.

- Consolidated rib-family and nexthop-address-family into a single
thing. They were simply duplicates.

- Got rid of fields nexthop-attributes. There was contention that
things like NO_PROPAGATE_TTL and NO_DECREMENT_TTL are too
implementation specific and shouldn't be in the info model. Since those
were only the only attributes currently present, there was no point in
having a nexthop-attr object that contained nothing.

- Got rid of the INSTANCE_DISTINGUISHER. It was a topic of great
discussion and everyone felt that INSTANCE_NAME and
INSTANCE_DISTINGUISHER were both the same thing (from a modeling
perspective). In the data-model, I think it still makes sense to have
the INSTANCE_DISTINGUISHER (a int value) as the key to the instance
list.

- Fixed numbering for the figures

- Added reference to multicast in the figures

- Got rid of route-metric…since there was no strong use-case for a
controller programming 2 routes with different metrics in the same RIB.

- Enhanced ipv4/ipv6 route object so as to enable source based routing.