net/mlx5e: CT: Fix ipv6 nat header rewrite actions

Set the ipv6 word fields according to the hardware definitions.

Fixes: ac991b48

 ("net/mlx5e: CT: Offload established flows")
Signed-off-by: Oz Shlomo <ozsh@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>