Cited patch deleted ethtool flash device support, as ethtool core can
fallback into devlink flash callback. However, this is supported only if
there is a devlink port registered over the corresponding netdevice.

As mlx5e do not have devlink port support over native netdevice, it broke
the ability to flash device via ethtool.

This patch re-add the ethtool callback to avoid user functionality breakage
when trying to flash device via ethtool.

Fixes: 9c8bca26 ("mlx5: Move firmware flash implementation to devlink")
Signed-off-by: Eran Ben Elisha <eranbe@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>