net/ncsi: Add NCSI Mellanox OEM command

This patch adds OEM Mellanox commands and response handling. It also
defines OEM Get MAC Address handler to get and configure the device.

ncsi_oem_gma_handler_mlx: This handler send NCSI mellanox command for
getting mac address.
ncsi_rsp_handler_oem_mlx: This handles response received for all
mellanox OEM commands.
ncsi_rsp_handler_oem_mlx_gma: This handles get mac address response and
set it to device.

Signed-off-by: Vijay Khemka <vijaykhemka@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>