net/mlx5: limit implicit MPLS RSS expansion over GRE

net/mlx5: limit implicit MPLS RSS expansion over GRE

As [1] optimized the MPLS RSS expansion before, this commit limits
the implicitly MPLS RSS expansion for MPLSoGRE as well. For the
RSS flow matcher to GRE level only, it will not expand the MPLS
match item for the sub flows due to performance consideration.

The original RSS flow match item:
ETH VLAN IPV6 GRE GRE_KEY END

The previous RSS expansion:
ETH VLAN IPV6 GRE GRE_KEY END
ETH VLAN IPV6 GRE GRE_KEY IPV4 END
ETH VLAN IPV6 GRE GRE_KEY MPLS IPV4 END
ETH VLAN IPV6 GRE GRE_KEY MPLS ETH IPV4 END

New RSS expansion:
ETH VLAN IPV6 GRE GRE_KEY END
ETH VLAN IPV6 GRE GRE_KEY IPV4 END

[1]
commit a26cc30fa046 ("net/mlx5: limit inner RSS expansion for MPLS")

Signed-off-by: Suanming Mou <suanmingm@nvidia.com>
Acked-by: Xiaoyu Min <jackmin@nvidia.com>
Acked-by: Matan Azrad <matan@nvidia.com>