IB/mlx5: Support MLX5_CMD_OP_QUERY_LAG as a DEVX general command

The "MLX5_CMD_OP_QUERY_LAG" is one of the DEVX general commands, add it.

Fixes: 8aa8c95c ("IB/mlx5: Add support for DEVX general command")
Signed-off-by: Mark Zhang <markz@mellanox.com>
Reviewed-by: Yishai Hadas <yishaih@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>