selftests/bpf: Add stacktrace ips test for kprobe_multi/kretprobe_multi

selftests/bpf: Add stacktrace ips test for kprobe_multi/kretprobe_multi

Adding test that attaches kprobe/kretprobe multi and verifies the
ORC stacktrace matches expected functions.

Adding bpf_testmod_stacktrace_test function to bpf_testmod kernel
module which is called through several functions so we get reliable
call path for stacktrace.

The test is only for ORC unwinder to keep it simple.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20251104215405.168643-4-jolsa@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>