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/act_csum.c b/net/sched/act_csum.c
index 67dc7ce..83ddfc0 100644
--- a/net/sched/act_csum.c
+++ b/net/sched/act_csum.c
@@ -508,8 +508,7 @@
 
 	spin_lock(&p->tcf_lock);
 	p->tcf_tm.lastuse = jiffies;
-	p->tcf_bstats.bytes += qdisc_pkt_len(skb);
-	p->tcf_bstats.packets++;
+	bstats_update(&p->tcf_bstats, skb);
 	action = p->tcf_action;
 	update_flags = p->update_flags;
 	spin_unlock(&p->tcf_lock);