asix: fix setting mac address for AX88772

Setting new MAC address only worked when device was set to promiscuous mode.
Fix MAC address by writing new address to device using undocumented command
AX_CMD_READ_NODE_ID+1. Patch is tested with AX88772 device.

Signed-off-by: Jussi Kivilinna <jussi.kivilinna@mbnet.fi>
Acked-by: David Hollis <dhollis@davehollis.com>
Signed-off-by: David S. Miller <davem@davemloft.net>