Merge branch 'selftests-bpf-test-btf-sanitization'

Alan Maguire says:

====================
selftests/bpf: Test BTF sanitization

Allow simulation of missing BPF features through provision of
a synthetic feature cache set, and use this to simulate case
where FEAT_BTF_LAYOUT is missing.  Ensure sanitization leaves us
with expected BTF (layout info removed, layout header fields
zeroed, strings data adjusted).

Specifying a feature cache with selected missing features will
allow testing of other missing feature codepaths, but for now
add BTF layout sanitization test only.

Changes since v2 [1]:

- change zfree() to free() since we immediately assign the
  feat_cache (Jiri, patch 1)
- "goto out" to avoid skeleton leak (Chengkaitao, patch 2)
- just use kfree_skb__open() since we do not need to load
  skeleton

Changes since v1 [2]:

- renamed to bpf_object_set_feat_cache() (Andrii, patch 1)
- remove __packed, relocate skeleton open/load, fix formatting
  issues (Andrii, patch 2)

[1] https://lore.kernel.org/bpf/20260408105324.663280-1-alan.maguire@oracle.com/
[2] https://lore.kernel.org/bpf/20260401164302.3844142-1-alan.maguire@oracle.com/
====================

Link: https://patch.msgid.link/20260408165735.843763-1-alan.maguire@oracle.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>