net/mlx5e: Add missing link mode to ptys2ext_ethtool_map

Add MLX5E_400GAUI_8_400GBASE_CR8 to the extended modes
in ptys2ext_ethtool_table, since it was missing.

Fixes: 6a897372 ("net/mlx5: ethtool, Add ethtool support for 50Gbps per lane link modes")
Signed-off-by: Shahar Shitrit <shshitrit@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Carolina Jubran <cjubran@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>