Merge branch 'bpf-add-kfunc-bpf_strncasecmp'

Yuzuki Ishiyama says:

====================
bpf: Add kfunc bpf_strncasecmp()

This patchset introduces bpf_strncasecmp to allow case-insensitive and
limited-length string comparison. This is useful for parsing protocol
headers like HTTP.
---

Changes in v5:
- Fixed the test function numbering

Changes in v4:
- Updated the loop variable to maintain style consistency

Changes in v3:
- Use ternary operator to maintain style consistency
- Reverted unnecessary doc comment about XATTR_SIZE_MAX

Changes in v2:
- Compute max_sz upfront and remove len check from the loop body
- Document that @len is limited by XATTR_SIZE_MAX
====================

Link: https://patch.msgid.link/20260121033328.1850010-1-ishiyama@hpc.is.uec.ac.jp
Signed-off-by: Alexei Starovoitov <ast@kernel.org>