net/mlx5e: Fix using wrong stats_grps in mlx5e_update_ndo_stats()

The cited commit started to reuse function mlx5e_update_ndo_stats() for
the representors as well.
However, the function is hard-coded to work on mlx5e_nic_stats_grps only.
Due to this issue, the representors statistics were not updated in the
output of "ip -s".

Fix it to work with the correct group by extracting it from the caller's
profile.

Also, while at it and since this function became generic, move it to
en_stats.c and rename it accordingly.

Fixes: 8a236b15

 ("net/mlx5e: Convert rep stats to mlx5e_stats_grp-based infra")
Signed-off-by: Alaa Hleihel <alaa@nvidia.com>
Reviewed-by: Vlad Buslov <vladbu@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>