net/mlx4_en: Use generic etherdevice.h functions.

Get rid of full_mac, zero_mac in favour of
is_zero_ether_addr and is_broadcast_ether_addr.

Signed-off-by: Yan Burman <yanb@mellanox.com>
Signed-off-by: Amir Vadai <amirv@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>