selftests/bpf: Allow to benchmark trigger with stacktrace

selftests/bpf: Allow to benchmark trigger with stacktrace

Adding support to call bpf_get_stackid helper from trigger programs,
so far added for kprobe multi.

Adding the --stacktrace/-g option to enable it.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20260126211837.472802-7-jolsa@kernel.org