pkt_sched: Fix return value corruption in HTB and TBF.

Based upon a bug report by Josip Rodin.

Packet schedulers should only return NET_XMIT_DROP iff
the packet really was dropped.  If the packet does reach
the device after we return NET_XMIT_DROP then TCP can
crash because it depends upon the enqueue path return
values being accurate.

Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/sched/sch_htb.c b/net/sched/sch_htb.c
index 6febd24..0df0df2 100644
--- a/net/sched/sch_htb.c
+++ b/net/sched/sch_htb.c
@@ -577,7 +577,7 @@
 			sch->qstats.drops++;
 			cl->qstats.drops++;
 		}
-		return NET_XMIT_DROP;
+		return ret;
 	} else {
 		cl->bstats.packets +=
 			skb_is_gso(skb)?skb_shinfo(skb)->gso_segs:1;
@@ -623,7 +623,7 @@
 			sch->qstats.drops++;
 			cl->qstats.drops++;
 		}
-		return NET_XMIT_DROP;
+		return ret;
 	} else
 		htb_activate(q, cl);