net/mlx5: Add support for QUERY_VNIC_ENV command

Add support for new FW command QUERY_VNIC_ENV.
The command is used by the driver to query vnic diagnostic statistics
from FW.

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