selftests/bpf: add benchmark testing for kprobe-multi-all

For now, the benchmark for kprobe-multi is single, which means there is
only 1 function is hooked during testing. Add the testing
"kprobe-multi-all", which will hook all the kernel functions during
the benchmark. And the "kretprobe-multi-all" is added too.

Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
Link: https://lore.kernel.org/r/20250904021011.14069-4-dongml2@chinatelecom.cn


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