net/mlx5e: Some cleanup in mlx5e_tc_stats_matchall()

Function mlx5e_tc_stats_matchall() is only called from one file:
drivers/net/ethernet/mellanox/mlx5/core/en/rep/tc.c
Move it there and make it static as exposing it is unnecessary. Also
variable cur_stats is redundant. Remove it and avoid superfluous copy.

This patch does not change functionality.

Reviewed-by: Patrisious Haddad <phaddad@nvidia.com>
Signed-off-by: Amir Tzin <amirtz@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>