[NET_SCHED]: Fix qdisc_restart return value when dequeue is empty

My previous patch that changed the return value of qdisc_restart
incorrectly made the case where dequeue returns empty continue
processing packets.

This patch is based on diagnosis and fix by Patrick McHardy.
Reported-and-debugged-by: NAnant Nitya <kernel@prachanda.info>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/sched/sch_generic.c

@@ -169,8 +169,8 @@ static inline int qdisc_restart(struct net_device *dev)
 		else
 			q->ops->requeue(skb, q);
 		netif_schedule(dev);
-		return 0;
 	}
+	return 0;
 
 out:
 	BUG_ON((int) q->q.qlen < 0);