net/mlx4: Add set VF mac address support

Add ndo_set_vf_mac support which allows to set the MAC address
for mlx4 VF Ethernet NICs from the host.

Signed-off-by: Rony Efraim <ronye@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>