net/mlx5e: Rename VPort counters

VPort and software counters names are confusing and may be unclear, all
VPort counters now have a prefix of rx/tx_vport_*.

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>