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_atm.c b/net/sched/sch_atm.c
index 2825407..943d733 100644
--- a/net/sched/sch_atm.c
+++ b/net/sched/sch_atm.c
@@ -422,10 +422,8 @@
 		}
 		return ret;
 	}
-	sch->bstats.bytes += qdisc_pkt_len(skb);
-	sch->bstats.packets++;
-	flow->bstats.bytes += qdisc_pkt_len(skb);
-	flow->bstats.packets++;
+	qdisc_bstats_update(sch, skb);
+	bstats_update(&flow->bstats, skb);
 	/*
 	 * Okay, this may seem weird. We pretend we've dropped the packet if
 	 * it goes via ATM. The reason for this is that the outer qdisc