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_ipt.c b/net/sched/act_ipt.c
index 8daef96..c2a7c20 100644
--- a/net/sched/act_ipt.c
+++ b/net/sched/act_ipt.c
@@ -209,8 +209,7 @@
 	spin_lock(&ipt->tcf_lock);
 
 	ipt->tcf_tm.lastuse = jiffies;
-	ipt->tcf_bstats.bytes += qdisc_pkt_len(skb);
-	ipt->tcf_bstats.packets++;
+	bstats_update(&ipt->tcf_bstats, skb);
 
 	/* yes, we have to worry about both in and out dev
 	 worry later - danger - this API seems to have changed