net_sched: factorize qdisc stats handling

HTB takes into account skb is segmented in stats updates.
Generalize this to all schedulers.

They should use qdisc_bstats_update() helper instead of manipulating
bstats.bytes and bstats.packets

Add bstats_update() helper too for classes that use
gnet_stats_basic_packed fields.

Note : Right now, TCQ_F_CAN_BYPASS shortcurt can be taken only if no
stab is setup on qdisc.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/sched/sch_cbq.c b/net/sched/sch_cbq.c
index eb76315..c80d1c2 100644
--- a/net/sched/sch_cbq.c
+++ b/net/sched/sch_cbq.c
@@ -390,8 +390,7 @@
 	ret = qdisc_enqueue(skb, cl->q);
 	if (ret == NET_XMIT_SUCCESS) {
 		sch->q.qlen++;
-		sch->bstats.packets++;
-		sch->bstats.bytes += qdisc_pkt_len(skb);
+		qdisc_bstats_update(sch, skb);
 		cbq_mark_toplevel(q, cl);
 		if (!cl->next_alive)
 			cbq_activate_class(cl);
@@ -650,8 +649,7 @@
 		ret = qdisc_enqueue(skb, cl->q);
 		if (ret == NET_XMIT_SUCCESS) {
 			sch->q.qlen++;
-			sch->bstats.packets++;
-			sch->bstats.bytes += qdisc_pkt_len(skb);
+			qdisc_bstats_update(sch, skb);
 			if (!cl->next_alive)
 				cbq_activate_class(cl);
 			return 0;