net/mlx5e: Add feature check for set fec counters

Fec counters support is checked via the PCAM feature_cap_mask,
bit 0: PPCNT_counter_group_Phy_statistical_counter_group.
Add feature check to avoid faulty behavior.

Fixes: 0a1498eb

 ("net/mlx5e: Expose FEC counters via ethtool")
Signed-off-by: Lama Kayal <lkayal@nvidia.com>
Reviewed-by: Gal Pressman <gal@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>