[AX25] ax25_timer: use mod_timer instead of add_timer

According to one of Jann's OOPS reports it looks like
BUG_ON(timer_pending(timer)) triggers during add_timer()
in ax25_start_t1timer(). This patch changes current use
of: init_timer(), add_timer() and del_timer() to
setup_timer() with mod_timer(), which should be safer
anyway.

Reported-by: Jann Traschewski <jann@gmx.de>
Signed-off-by: Jarek Poplawski <jarkao2@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c
index 5a4337a..48bfcc7 100644
--- a/net/ax25/af_ax25.c
+++ b/net/ax25/af_ax25.c
@@ -510,11 +510,7 @@
 	skb_queue_head_init(&ax25->ack_queue);
 	skb_queue_head_init(&ax25->reseq_queue);
 
-	init_timer(&ax25->timer);
-	init_timer(&ax25->t1timer);
-	init_timer(&ax25->t2timer);
-	init_timer(&ax25->t3timer);
-	init_timer(&ax25->idletimer);
+	ax25_setup_timers(ax25);
 
 	ax25_fillin_cb(ax25, NULL);