net/mlx4_en: Implement ndo_get_phys_port_id

Use the port GUID read from the firmware to identify the physical port.
This port identifier is available via ndo_get_phys_port_id for both PF
and VF net-devices.

Signed-off-by: Hadar Hen Zion <hadarh@mellanox.com>
Signed-off-by: Amir Vadai <amirv@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>