net/mlx5: fix RSS expansion for inner tunnel VLAN

net/mlx5: fix RSS expansion for inner tunnel VLAN

The RSS expansion algorithm is using a graph to find the possible
expansion paths. The VLAN item in the flow pattern requires special
treatment, because it should not be added implicitly by the expansion
algorithm.  If the flow pattern ends with ETH item, the pattern will be
expanded with IPv4 and IPv6.
For example:
testpmd> flow create ... eth / end actions rss / end
ETH END
ETH IPV4 END
ETH IPV6 END
If a VLAN item follows the ETH item in the flow pattern, the pattern
will be expanded with IPv4 and IPv6 following the VLAN item.
For example:
testpmd> flow create ... eth / vlan / end actions rss level 1 / end
ETH VLAN END
ETH VLAN IPV4 END
ETH VLAN IPV6 END

The case of inner tunnel VLAN item was not taken care of so the flow
pattern did not expand with IPv6 and IPv4 as expected.
Example with inner VLAN:
testpmd> flow create ... / vxlan / eth / vlan / end actions rss level 2
/ end
The current result of the expansion alg:
ETH IPV6 UDP VXLAN ETH VLAN END
The expected result of the expansion alg:
ETH IPV6 UDP VXLAN ETH VLAN END
ETH IPV6 UDP VXLAN ETH VLAN IPV4 END
ETH IPV6 UDP VXLAN ETH VLAN IPV6 END

The fix is to introduce a new flag to set on a graph expansion node
to apply the 'explicit' behavior, meaning the node is not added to
the expanded pattern, if it is not found in the flow pattern, but the
expansion alg can go deeper to its next nodes.

Fixes: c7870bfe09dc ("ethdev: move RSS expansion code to mlx5 driver")
Cc: stable@dpdk.org
Signed-off-by: Lior Margalit <lmargalit@nvidia.com>
Acked-by: Matan Azrad <matan@nvidia.com>