net/mlx5: fix MPLS RSS expansion

net/mlx5: fix MPLS RSS expansion

MPLSoUDP and MPLSoGRE are supported by PMD from
rte flow point of view.

RSS expansion doesn't support above but, instead, supports
normal MPLS over L2, which actually will be rejected by PMD.

This patch removes RSS expansion support of the MPLS over L2
and adds support of MPLSoUDP and MPLSoGRE.

In addition to above, support for eth over MPLS expansion is
added too.

Fixes: a4a5cd21d20a ("net/mlx5: add flow MPLS item")
Cc: stable@dpdk.org
Signed-off-by: Xiaoyu Min <jackmin@nvidia.com>
Acked-by: Matan Azrad <matan@nvidia.com>