net/mlx5e: aRFS, Introduce ethtool stats

Improve aRFS observability by adding new set of counters. Each Rx
ring will have this set of counters listed below.
These counters are exposed through ethtool -S.

1) arfs_add: number of times a new rule has been created.
2) arfs_request_in: number of times a rule  was requested to move from
   its current Rx ring to a new Rx ring (incremented on the destination
   Rx ring).
3) arfs_request_out: number of times a rule  was requested to move out
   from its current Rx ring (incremented on source/current Rx ring).
4) arfs_expired: number of times a rule has been expired by the
   kernel and removed from HW.
5) arfs_err: number of times a rule creation or modification has
   failed.

This patch removes rx[i]_xsk_arfs_err counter and its documentation in
mlx5/counters.rst since aRFS activity does not occur in XSK RQ's.

Signed-off-by: Adham Faris <afaris@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Reviewed-by: Shay Drory <shayd@nvidia.com>