net/mlx5: fix MPLS tunnel outer layer overwrite

net/mlx5: fix MPLS tunnel outer layer overwrite

mlx5 PMD incorrectly overwrote outer layer fields in MPLS tunnel
rte_flow patterns using defaults for MPLS tunnels. This included
overwriting UDP destination port in MPLSoUDP and GRE protocol field in
MPLSoGRE.

This patch fixes this behavior. If application provides the values in
flow pattern items preceding the MPLS flow item the provided values will
be used, otherwise the defaults will be applied.

Fixes: d1abe664ddde ("net/mlx5: add MPLS to Direct Verbs flow engine")
Cc: stable@dpdk.org
Signed-off-by: Dariusz Sosnowski <dsosnowski@nvidia.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>