NET: AX.25: Stop heartbeat timer on disconnect.

This may result in a kernel panic.  The bug has always existed but
somehow we've run out of luck now and it bites.
Signed-off-by: NRichard Stearn <richard@rns-stearn.demon.co.uk>
Cc: stable@vger.kernel.org	# all branches
Signed-off-by: NRalf Baechle <ralf@linux-mips.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ax25/ax25_subr.c

@@ -264,6 +264,7 @@ void ax25_disconnect(ax25_cb *ax25, int reason)
 {
 	ax25_clear_queues(ax25);
 
+	ax25_stop_heartbeat(ax25);
 	ax25_stop_t1timer(ax25);
 	ax25_stop_t2timer(ax25);
 	ax25_stop_t3timer(ax25);