lib: route-table improvements.

lib: route-table improvements.

This commit makes several changes to the route_table code used to
populate tunnel_egress_iface.

- It removes name_table code from netdev-vport and puts it into
  route-table.

- It no longer attempts to build the name_table dynamically by
  listening to rtnetlink-link notifications.  Instead it dumps the
  entire table, and uses rtnetlink-link notifications to indicate a
  re-dump is required.

- It forces rtnetlink-link notifications to re-dump the routing
  table.  This fixes an issue where bringing an interface down or
  removing it altogether would not have the expected effect on
  related tunnel_egress_ifaces.