pkt_sched: Fix locking in shutdown_scheduler_queue()

Qdisc locks need to be held with BH disabled.
Tested-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_generic.c

@@ -736,9 +736,9 @@ static void shutdown_scheduler_queue(struct net_device *dev,
 		dev_queue->qdisc = qdisc_default;
 		dev_queue->qdisc_sleeping = qdisc_default;
 
-		spin_lock(root_lock);
+		spin_lock_bh(root_lock);
 		qdisc_destroy(qdisc);
-		spin_unlock(root_lock);
+		spin_unlock_bh(root_lock);
 	}
 }