net/mlx5e: Don't query FEC statistics when FEC is disabled

Update mlx5e_stats_fec_get() to check the active FEC mode and skip
statistics collection when FEC is disabled.

Signed-off-by: Carolina Jubran <cjubran@nvidia.com>
Reviewed-by: Dragos Tatulea <dtatulea@nvidia.com>
Reviewed-by: Yael Chemla <ychemla@nvidia.com>
Signed-off-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Link: https://patch.msgid.link/20250924124037.1508846-3-vadim.fedorenko@linux.dev


Signed-off-by: Jakub Kicinski <kuba@kernel.org>