Fixes a tricky bug in the pipe protocol.

Fixes a tricky bug in the pipe protocol.

When uncofiguring the pipe and the peer table, the peer table was
unlocked when pipe protocol state changed to down/flushing and not to
down/hungry. This leads to the removal of the peer table before
the routes from the pipe were flushed.

The fix leads to adding some pipe-specific hacks to the nest,
but this seems inevitable.