netpoll: Convert printks to np_<level> and add pr_fmt

Use a more current message logging style.
Add pr_fmt to prefix dmesg output with "netpoll: "
Add macros to print np->name.

Signed-off-by: Joe Perches <joe@perches.com>
Reviewed-by: WANG Cong <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>