cc: libbpf: Fix ambiguous comment

When creating [k,u]probe, comment above bpf_try_perf_event_open_with_probe()
said "new kernel API".

"new" is a relative concept and it's committed at f180ea1
("bcc: add functions to use new [k,u]probe API"), it's not "new" now.

The "new" API came from
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e12f03d

Remove "new" word and explicit provide which commit in the Linux kernel is.

src/cc/libbpf.c

@@ -751,9 +751,9 @@ static int bpf_get_retprobe_bit(const char *event_type)
 }
 
 /*
- * new kernel API allows creating [k,u]probe with perf_event_open, which
- * makes it easier to clean up the [k,u]probe. This function tries to
- * create pfd with the new API.
+ * Kernel API with e12f03d ("perf/core: Implement the 'perf_kprobe' PMU") allows
+ * creating [k,u]probe with perf_event_open, which makes it easier to clean up
+ * the [k,u]probe. This function tries to create pfd with the perf_kprobe PMU.
  */
 static int bpf_try_perf_event_open_with_probe(const char *name, uint64_t offs,
  int pid, const char *event_type, int is_return)
@@ -941,7 +941,6 @@ static int create_probe_event(char *buf, const char *ev_name,
  bool is_kprobe = strncmp("kprobe", event_type, 6) == 0;
 
  snprintf(buf, PATH_MAX, "/sys/kernel/debug/tracing/%s_events", event_type);
-
  kfd = open(buf, O_WRONLY | O_APPEND, 0);
  if (kfd < 0) {
  fprintf(stderr, "%s: open(%s): %s\n", __func__, buf,
@@ -1013,8 +1012,9 @@ static int bpf_attach_probe(int progfd, enum bpf_probe_attach_type attach_type,
  pfd = bpf_try_perf_event_open_with_probe(config1, offset, pid, event_type,
  attach_type != BPF_PROBE_ENTRY);
 
- // If failed, most likely Kernel doesn't support the new perf_event_open API
- // yet. Try create the event using debugfs.
+ // If failed, most likely Kernel doesn't support the perf_kprobe PMU
+ // (e12f03d "perf/core: Implement the 'perf_kprobe' PMU") yet.
+ // Try create the event using debugfs.
  if (pfd < 0) {
  if (create_probe_event(buf, ev_name, attach_type, config1, offset,
  event_type, pid, maxactive) < 0)