peer_fail_permanent() frees peer->owner, but for bad_peer() we're
being called by the sd->badpeercb(), which then goes on to
io_close(conn) which is a child of sd.
We need to detach the two for this case, so neither tries to free the
other.
This leads to a corner case when the subd exits after the peer is gone:
subd->peer is NULL, so we have to handle that too.
Fixes: #282
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
2fe2a0bcf9