netpoll_send_skb_on_dev() can get the device pointer directly from np->dev

Rename it to __netpoll_send_skb()

Following patch will move netpoll_send_skb() out-of-line.
Signed-off-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>