Merge branch 'bpf-support-bpf-rbtree-traversal-and-list-peeking'

Martin KaFai Lau says:

====================
bpf: Support bpf rbtree traversal and list peeking

From: Martin KaFai Lau <martin.lau@kernel.org>

The RFC v1 [1] showed a fq qdisc implementation in bpf
that is much closer to the kernel sch_fq.c.

The fq example and bpf qdisc changes are separated out from this set.
This set is to focus on the kfunc and verifier changes that
enable the bpf rbtree traversal and list peeking.

v2:
- Added tests to check that the return value of
  the bpf_rbtree_{root,left,right} and bpf_list_{front,back} is
  marked as a non_own_ref node pointer. (Kumar)
- Added tests to ensure that the bpf_rbtree_{root,left,right} and
  bpf_list_{front,back} must be called after holding the spinlock.
- Squashed the selftests adjustment to the corresponding verifier
  changes to avoid bisect failure. (Kumar)
- Separated the bpf qdisc specific changes and fq selftest example
  from this set.

[1]: https://lore.kernel.org/bpf/20250418224652.105998-1-martin.lau@linux.dev/
====================

Link: https://patch.msgid.link/20250506015857.817950-1-martin.lau@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>