net/mlx5: fix GENEVE and VXLAN-GPE flow item matching

net/mlx5: fix GENEVE and VXLAN-GPE flow item matching

GENEVE and VXLAN-GPE item matching is done similarly to GRE matching.
Users can skip the specification of the protocol type and expect that
this type is deducted from the inner header type automatically.
But the inner header type may not be specified in order to match all the
protocol types. In this case, PMD should not specify the protocol type.
Check if we have the inner header type before setting the protocol type.

Fixes: 690391dd0e8b ("net/mlx5: fix GENEVE protocol type translation")
Fixes: 861fa3796f75 ("net/mlx5: fix VXLAN-GPE next protocol translation")
Cc: stable@dpdk.org
Signed-off-by: Alexander Kozyrev <akozyrev@nvidia.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>