selftests/bpf: Allow VLAN packets in xdp_hw_metadata

Make VLAN c-tag and s-tag XDP hint testing more convenient
by not skipping VLAN-ed packets.

Allow both 802.1ad and 802.1Q headers.

Acked-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Larysa Zaremba <larysa.zaremba@intel.com>
Link: https://lore.kernel.org/r/20231205210847.28460-16-larysa.zaremba@intel.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>