net/mlx5e: Add support for ethtool msglvl support

Use ethtool -s <devname> msglvl <type> on/off to toggle debug messages.

Signed-off-by: Gal Pressman <galp@mellanox.com>
Signed-off-by: Inbar Karmy <inbark@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>