sch_red: report backlog information

Provide child qdisc backlog (byte count) information so that "tc -s
qdisc" can report it to user.

packet count is already correctly provided.

qdisc red 11: parent 1:11 limit 60Kb min 15Kb max 45Kb ecn
 Sent 3116427684 bytes 1415782 pkt (dropped 8, overlimits 7866 requeues 0)
 rate 242385Kbit 13630pps backlog 13560b 8p requeues 0
  marked 7865 early 1 pdrop 7 other 0
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_red.c

@@ -239,6 +239,7 @@ static int red_dump(struct Qdisc *sch, struct sk_buff *skb)
 		.Scell_log	= q->parms.Scell_log,
 	};
 
+	sch->qstats.backlog = q->qdisc->qstats.backlog;
 	opts = nla_nest_start(skb, TCA_OPTIONS);
 	if (opts == NULL)
 		goto nla_put_failure;