pkt_sched: Never schedule non-root qdiscs.

Based upon initial discovery and patch by Jarek Poplawski.

The qdisc watchdogs can be attached to any qdisc, not just the root,
so make sure we schedule the correct one.

CBQ has a similar bug.

Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index c8dc72e..98c0084 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -426,7 +426,7 @@
 
 	wd->qdisc->flags &= ~TCQ_F_THROTTLED;
 	smp_wmb();
-	__netif_schedule(wd->qdisc);
+	__netif_schedule(qdisc_root(wd->qdisc));
 
 	return HRTIMER_NORESTART;
 }