samples/bpf: use bpf_prog_query() interface

use BPF_PROG_QUERY command to strengthen test coverage

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>