net-sched: fix bfifo default limit

When no limit is given, the bfifo uses a default of tx_queue_len * mtu.
Packets handled by qdiscs include the link layer header, so this should
be taken into account, similar to what other qdiscs do.

Signed-off-by: Patrick McHardy <kaber@trash.net>

diff --git a/net/sched/sch_fifo.c b/net/sched/sch_fifo.c
index 92cfc9d..69188e8 100644
--- a/net/sched/sch_fifo.c
+++ b/net/sched/sch_fifo.c
@@ -51,7 +51,7 @@ static int fifo_init(struct Qdisc *sch, struct nlattr *opt)
 		u32 limit = qdisc_dev(sch)->tx_queue_len ? : 1;
 
 		if (sch->ops == &bfifo_qdisc_ops)
-			limit *= qdisc_dev(sch)->mtu;
+			limit *= psched_mtu(qdisc_dev(sch));
 
 		q->limit = limit;
 	} else {