net/mlx5: Add packet dropped while vport down statistics

Added the following packets dropped while vport down statistics:

Rx dropped while vport down - counts packets which were steered by
e-switch to a vport, but dropped since the vport was down. This counter
will be shown on ip link tool as part of the vport rx_dropped counter.

Tx dropped while vport down - counts packets which were transmitted by
a vport, but dropped due to vport logical link down. This counter
will be shown on ip link tool as part of the vport tx_dropped counter.

The counters are read from FW by command QUERY_VNIC_ENV.

Signed-off-by: Moshe Shemesh <moshe@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>