net/mlx5: allow copy from one tag to another

net/mlx5: allow copy from one tag to another

The modify field implementation in mlx5 driver has a check to
prevent a copy from a field to the same field. But the level
is not taken into account which prevents a copy from different
tags. Check the level and allow a copy from one tag to another.

Fixes: 641dbe4fb05 ("net/mlx5: support modify field flow action")
Cc: stable@dpdk.org
Signed-off-by: Alexander Kozyrev <akozyrev@nvidia.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>