net/mlx5e: Add HW vport counters to representor ethtool stats

Currently the representor only report the SW (slow-path) traffic
counters.

Add packet/bytes reporting of the HW counters, which account for the
total amount of traffic that was handled by the vport, both slow and
fast (offloaded) paths. The newly exposed counters are named
vport_rx/tx_packets/bytes.

Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Adi Nissim <adin@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>