selftests/bpf: Add tests for may_goto with negative offset.

Add few tests with may_goto and negative offset.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20240619235355.85031-2-alexei.starovoitov@gmail.com