protocol callbacks for route insertion and deletion from the central table.
RIP should maintain its own per-protocol queue of existing routes, scan it
periodically and call rte_discard() for routes that have timed out.
loop detection. This is needed since both RIP and OSPF handle multiple
neighbors and they need to redistribute routes learned from each neighbor
to the remaining ones.
protocols and don't send route/interface updates to them and when they come up,
we resend the whole route/interface tables privately.
Removed the "scan interface list after protocol start" work-around.
