on each of them, and don't bother listening on them. this allows messages
to be forwarded even with -s enabled.
XXX: not 100% sure if this is susceptable to a DoS, e.g someone filling
up kernel buffers with a backlog of packets not being read, but shutdown(2)
should prevent that even if it possibly doesn't at this time.
* minor KNF
315a29d6de