selftests/bpf: Add test for bpf_obj_drop with bad reg->off

Add a selftest for the fix provided in the previous commit. Without the
fix, the selftest passes the verifier while it should fail. The special
logic for detecting graph root or node for reg->off and bypassing
reg->off == 0 guarantee for release helpers/kfuncs has been dropped.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20230822175140.1317749-3-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

selftests/bpf: Add a failure test for bpf_kptr_xchg() with local kptr

For a bpf_kptr_xchg() with local kptr, if the map value kptr type and
allocated local obj type does not match, with the previous patch,
the below verifier error message will be logged:
R2 is of type <allocated local obj type> but <map value kptr type> is expected

Without the previous patch, the test will have unexpected success.

Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20230822050058.2887354-1-yonghong.song@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>