net: introduce dev_consume_skb_any()

Some network drivers use dev_kfree_skb_any() and dev_kfree_skb_irq()
helpers to free skbs, both for dropped packets and TX completed ones.

We need to separate the two causes to get better diagnostics
given by dropwatch or "perf record -e skb:kfree_skb"

This patch provides two new helpers, dev_consume_skb_any() and
dev_consume_skb_irq() to be used for consumed skbs.

__dev_kfree_skb_irq() is slightly optimized to remove one
atomic_dec_and_test() in fast path, and use this_cpu_{r|w} accessors.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>