net/mlx5: fix RSS expansion for L2/L3 VXLAN

net/mlx5: fix RSS expansion for L2/L3 VXLAN

The RSS expansion algorithm is using a graph to find the possible
expansion paths. The current implementation does not differentiate
between standard (L2) VXLAN and L3 VXLAN. As result the flow is expanded
with all possible paths.
For example:
testpmd> flow create... / vxlan / end actions rss level 2 / end
It is currently expanded to the following paths:
ETH IPV4 UDP VXLAN END
ETH IPV4 UDP VXLAN ETH IPV4 END
ETH IPV4 UDP VXLAN ETH IPV6 END
ETH IPV4 UDP VXLAN IPV4 END
ETH IPV4 UDP VXLAN IPV6 END

The fix is to adjust the expansion according to the outer UDP destination
port. In case flow pattern defines a match on the standard udp port, 4789,
or does not define a match on the destination port, which also implies
setting the standard one, the expansion for the above example will be:
ETH IPV4 UDP VXLAN END
ETH IPV4 UDP VXLAN ETH IPV4 END
ETH IPV4 UDP VXLAN ETH IPV6 END
Otherwise, the expansion will be:
ETH IPV4 UDP VXLAN END
ETH IPV4 UDP VXLAN IPV4 END
ETH IPV4 UDP VXLAN IPV6 END

Fixes: f4f06e361516 ("net/mlx5: add flow VXLAN item")
Cc: stable@dpdk.org
Signed-off-by: Lior Margalit <lmargalit@nvidia.com>
Acked-by: Matan Azrad <matan@nvidia.com>