Implement decoding of BPF_PROG_TEST_RUN command of bpf syscall

Implement decoding of BPF_PROG_TEST_RUN command of bpf syscall

* configure.ac: Check for union bpf_attr.test.duration.
* bpf.c (decode_BPF_PROG_TEST_RUN): New function.
(SYS_FUNC(bpf)) <bpf_cmd_decoders>: Use it.
* NEWS: Mention this.
* tests/bpf.c: Include "print_fields.h".
Add macro guard for BPF_PROG_TEST_RUN decoder test.
[HAVE_UNION_BPF_ATTR_TEST_DURATION] (sample_BPF_PROG_TEST_RUN_attr):
New variable.
[HAVE_UNION_BPF_ATTR_TEST_DURATION] (init_BPF_PROG_TEST_RUN_first,
print_BPF_PROG_TEST_RUN_first, init_BPF_PROG_TEST_RUN_attr,
print_BPF_PROG_TEST_RUN_attr): New functions.
(main) [HAVE_UNION_BPF_ATTR_TEST_DURATION]: Use them.