Remove the rdomain / rtableid passed to some kroute functions.

Remove the rdomain / rtableid passed to some kroute functions.

kr_nexthop_add() and kr_nexthop_delete() only operate on the main table
so just pass in the right rdomain id.
kr_shutdown() and kr_dispatch_msg() don't really need the rdomain passed.
The was done for kif_remove(), since that function needs to remove connected
routes from the rdomain table. Connected routes can only exists in the
interfaces rdomain so just use kif->k.rdomain. If such routes exist that
table exists as well. If the table does not exists there are also no
connected routes to track.
OK tb@