net/mlx4_en: Use HW counters for rx/tx bytes/packets in PF device

Under SRIOV, the port rx/tx bytes/packets statistics should by read
from the HW instead of using the PF netdevice SW accounting. This is
needed in order to get the full port statistics and not just the PF
own ones

Signed-off-by: Eran Ben Elisha <eranbe@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>