pkt_sched: Fix locking in shutdown_scheduler_queue()

Qdisc locks need to be held with BH disabled.

Tested-by: Ingo Molnar <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/sched/sch_generic.c

···
 		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);
 	}
 }