selftests/bpf: Add tests for raw_tp null handling

[ Upstream commit d798ce3f4cab1b0d886b19ec5cc8e6b3d7e35081 ]

Ensure that trusted PTR_TO_BTF_ID accesses perform PROBE_MEM handling in
raw_tp program. Without the previous fix, this selftest crashes the
kernel due to a NULL-pointer dereference. Also ensure that dead code
elimination does not kick in for checks on the pointer.

Reviewed-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20241104171959.2938862-4-memxor@gmail.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Stable-dep-of: 5da7e15fb5a1 ("net: Add rx_skb of kfree_skb to raw_tp_null_args[].")
Signed-off-by: Sasha Levin <sashal@kernel.org>