net/mlx5: fix layer flags missing in metadata

net/mlx5: fix layer flags missing in metadata

Metadata suffix subflow inherits the RSS needed hash_fields from the
prefix subflow as the suffix subflow only has the tag match item unable
to generate the full original hash_fields for RSS action.

Unfortunately, hash_fields will only be generated if flow has RSS
action. So it means the prefix flow won't generate the hash_fields as
the RSS action has been split to the suffix flow.

Copy the layer flags from prefix subflow to suffix subflow to help the
suffix subflow to generate the correct hash_fields itself.

Fixes: 71e254bc0294 ("net/mlx5: split Rx flows to provide metadata copy")
Cc: stable@dpdk.org
Signed-off-by: Suanming Mou <suanmingm@mellanox.com>
Acked-by: Matan Azrad <matan@mellanox.com>