net/mlx5e: IPoIB, Support the flash device ethtool callback

This callback further invokes the mlxfw module to flash the new
firmware file to the device.

Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Yotam Gigi <yotamg@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>