I reviewed, patched, and tested ppp_async.c to implement
ldisc->hangup().  This correctly terminates the PPP connection on
hangup.

Paul Mackerras already did an excellent job of ensuring safe shutdown
and I/O completion in ldisc->close so the change is trivial: just add
the ldisc->hangup and call the existing close routine.

Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>