selftests/bpf: Filter out default_idle from kprobe_multi bench

selftests/bpf: Filter out default_idle from kprobe_multi bench

Alexei hit following rcu warning when running prog_test -j.

  [  128.049567] WARNING: suspicious RCU usage
  [  128.049569] 6.1.0-rc2 #912 Tainted: G           O
  ...
  [  128.050944]  kprobe_multi_link_handler+0x6c/0x1d0
  [  128.050947]  ? kprobe_multi_link_handler+0x42/0x1d0
  [  128.050950]  ? __cpuidle_text_start+0x8/0x8
  [  128.050952]  ? __cpuidle_text_start+0x8/0x8
  [  128.050958]  fprobe_handler.part.1+0xac/0x150
  [  128.050964]  0xffffffffa02130c8
  [  128.050991]  ? default_idle+0x5/0x20
  [  128.050998]  default_idle+0x5/0x20

It's caused by bench test attaching kprobe_multi link to default_idle
function, which is not executed in rcu safe context so the kprobe
handler on top of it will trigger the rcu warning.

Filtering out default_idle function from the bench test.

Reported-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20221116100228.2064612-1-jolsa@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>