net/mlx5: fix VLAN ID action offset

net/mlx5: fix VLAN ID action offset

Currently, the set VLAN ID header modify action has already got the
action pointer with offset from the header modify action array, but
the configuration saves the detail to the memory of action with the
offset again. It causes double offset to set the VLAN ID action to
the wrong place in the header modify array.

Remove the offset when get the action pointer to fix that issue.

Fixes: 5f163d520cff ("net/mlx5: support modify VLAN ID on existing VLAN header")
Cc: stable@dpdk.org
Signed-off-by: Suanming Mou <suanmingm@mellanox.com>
Acked-by: Dekel Peled <dekelp@mellanox.com>
Acked-by: Matan Azrad <matan@mellanox.com>