net/mlx5: ethtool, Add ethtool support for 50Gbps per lane link modes

In previous patch, driver added new speed modes: 50Gbps per lane support
for 50G/100G/200G.  This patch modifies mlx5e_get_link_ksettings and
mlx5e_set_link_ksettings to set and get these link modes via ethtool.
In order to do so, added mapping of new HW bits to ethtool bitmap and
enforce mutual exclusion between extended link modes and previously
defined link modes.

Signed-off-by: Aya Levin <ayal@mellanox.com>
Reviewed-by: Eran Ben Elisha <eranbe@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>