selftests/bpf: Add kprobe_multi check to module attach test

Adding test that makes sure the kernel module won't be removed
if there's kprobe multi link defined on top of it.

Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20221025134148.3300700-8-jolsa@kernel.org


Signed-off-by: Alexei Starovoitov <ast@kernel.org>