selftests/bpf: Add test for abnormal cnt during multi-uprobe attachment

If an abnormally huge cnt is used for multi-uprobes attachment, the
following warning will be reported:

  ------------[ cut here ]------------
  WARNING: CPU: 7 PID: 406 at mm/util.c:632 kvmalloc_node+0xd9/0xe0
  Modules linked in: bpf_testmod(O)
  CPU: 7 PID: 406 Comm: test_progs Tainted: G ...... 6.7.0-rc3+ #32
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996) ......
  RIP: 0010:kvmalloc_node+0xd9/0xe0
  ......
  Call Trace:
   <TASK>
   ? __warn+0x89/0x150
   ? kvmalloc_node+0xd9/0xe0
   bpf_uprobe_multi_link_attach+0x14a/0x480
   __sys_bpf+0x14a9/0x2bc0
   do_syscall_64+0x36/0xb0
   entry_SYSCALL_64_after_hwframe+0x6e/0x76
   ......
   </TASK>
  ---[ end trace 0000000000000000 ]---

So add a test to ensure the warning is fixed.

Signed-off-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20231215100708.2265609-4-houtao@huaweicloud.com