net/mlx5e: Reorganize ethtool statistics

Categorize and reorganize ethtool statistics counters by renaming to
"rx_*" and "tx_*" and removing redundant and duplicated counters, this
way they are easier to grasp and more user friendly.

Signed-off-by: Gal Pressman <galp@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>