macvlan: add netpoll support

Add netpoll support to macvlan devices. Based on the netpoll support in the 802.1q vlan code.

Tested and macvlan could work well with netconsole.

Signed-off-by: Ding Tianhong <dingtianhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>