mlx4_en: Move to SW counters for total bytes and packets

The per ring counters are implemented in SW. Now moving to have the total
counters as the sum of all rings. This way the numbers will always be consistent
and we no longer depend on HW buffer size limitations for those counters
that can be insufficient in some cases.

Signed-off-by: Yevgeny Petrilin <yevgenyp@mellanox.co.il>
Signed-off-by: David S. Miller <davem@davemloft.net>