samples/bpf: fix build by setting HAVE_ATTR_TEST to zero

To remove that test_attr__{enabled/open} are used by perf-sys.h, we
set HAVE_ATTR_TEST to zero.

Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Tested-by: KP Singh <kpsingh@google.com>
Acked-by: Song Liu <songliubraving@fb.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: bpf@vger.kernel.org
Cc: netdev@vger.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: http://lore.kernel.org/bpf/20191001113307.27796-3-bjorn.topel@gmail.com