netem: Fix off-by-one bug in reordering

With netem reordering, a gap of N is supposed to reorder every Nth packet with
given reorder probability.  However, the code currently skips N packets and
reorders every (N+1)th packet.
Signed-off-by: Vijay Subramanian <subramanian.vijay@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_netem.c

@@ -419,7 +419,7 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch)
 
 	cb = netem_skb_cb(skb);
 	if (q->gap == 0 ||		/* not doing reordering */
-	    q->counter < q->gap ||	/* inside last reordering gap */
+	    q->counter < q->gap - 1 ||	/* inside last reordering gap */
 	    q->reorder < get_crandom(&q->reorder_cor)) {
 		psched_time_t now;
 		psched_tdiff_t delay;