net/mlx5e: Expose FEC counters via ethtool

Add FEC counters' statistics of corrected_blocks and
uncorrectable_blocks, along with their lanes via ethtool.

HW supports corrected_blocks and uncorrectable_blocks counters both for
RS-FEC mode and FC-FEC mode. In FC mode these counters are accumulated
per lane, while in RS mode the correction method crosses lanes, thus
only total corrected_blocks and uncorrectable_blocks are reported in
this mode.

Signed-off-by: Lama Kayal <lkayal@nvidia.com>
Reviewed-by: Gal Pressman <gal@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>