selftests/bpf: Split test_attach_probe into multi subtests

In order to adapt to the older kernel, now we split the "attach_probe"
testing into multi subtests:

  manual // manual attach tests for kprobe/uprobe
  auto // auto-attach tests for kprobe and uprobe
  kprobe-sleepable // kprobe sleepable test
  uprobe-lib // uprobe tests for library function by name
  uprobe-sleepable // uprobe sleepable test
  uprobe-ref_ctr // uprobe ref_ctr test

As sleepable kprobe needs to set BPF_F_SLEEPABLE flag before loading,
we need to move it to a stand alone skel file, in case of it is not
supported by kernel and make the whole loading fail.

Therefore, we can only enable part of the subtests for older kernel.

Signed-off-by: Menglong Dong <imagedong@tencent.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Biao Jiang <benbjiang@tencent.com>
Link: https://lore.kernel.org/bpf/20230306064833.7932-3-imagedong@tencent.com