lib: Simplify rtnetlink routing functionality.

lib: Simplify rtnetlink routing functionality.

This commit removes the rtnetlink-route module and replaces it with
a much simpler to use route-table module.  The route-table uses
rtnetlink to maintain a routing table which may be used to query
the egress interface of particular addresses.

This commit also converts netdev-vport to use the new route-table
module.