bpf: Allow return values 0 and 1 for kprobe session

The kprobe session program can return only 0 or 1,
instruct verifier to check for that.

Fixes: 535a3692 ("bpf: Add support for kprobe session attach")
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20241108134544.480660-2-jolsa@kernel.org