net: validate_xmit_skb() changes

skbs given to validate_xmit_skb() should not have a next
pointer anymore.

Also if a packet is dropped, increment dev->tx_dropped
__dev_queue_xmit() no longer has to change tx_dropped in this case.

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