selftests/bpf: add test for bpf_xdp_query xdp-features support

Introduce a self-test to verify libbpf bpf_xdp_query capability to dump
the xdp-features supported by the device (lo and veth in this case).

Acked-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://lore.kernel.org/r/534550318a2c883e174811683909544c63632f05.1675245258.git.lorenzo@kernel.org


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