libbpf: Avoid designated initializers for unnamed union members

As it fails to build in some systems with:

  libbpf.c: In function 'perf_buffer__new':
  libbpf.c:4515: error: unknown field 'sample_period' specified in initializer
  libbpf.c:4516: error: unknown field 'wakeup_events' specified in initializer

Doing as:

    attr.sample_period = 1;

I.e. not as a designated initializer makes it build everywhere.

Cc: Andrii Nakryiko <andriin@fb.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Fixes: fb84b822 ("libbpf: add perf buffer API")
Link: https://lkml.kernel.org/n/tip-hnlmch8qit1ieksfppmr32si@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/lib/bpf/libbpf.c

@@ -4519,13 +4519,13 @@ struct perf_buffer *perf_buffer__new(int map_fd, size_t page_cnt,
 				     const struct perf_buffer_opts *opts)
 {
 	struct perf_buffer_params p = {};
-	struct perf_event_attr attr = {
-		.config = PERF_COUNT_SW_BPF_OUTPUT,
-		.type = PERF_TYPE_SOFTWARE,
-		.sample_type = PERF_SAMPLE_RAW,
-		.sample_period = 1,
-		.wakeup_events = 1,
-	};
+	struct perf_event_attr attr = { 0, };
+
+	attr.config = PERF_COUNT_SW_BPF_OUTPUT,
+	attr.type = PERF_TYPE_SOFTWARE;
+	attr.sample_type = PERF_SAMPLE_RAW;
+	attr.sample_period = 1;
+	attr.wakeup_events = 1;
 
 	p.attr = &attr;
 	p.sample_cb = opts ? opts->sample_cb : NULL;