Merge branch 'check-bpf_func_state-callback_depth-when-pruning-states'

Eduard Zingerman says:

====================
check bpf_func_state->callback_depth when pruning states

This patch-set fixes bug in states pruning logic hit in mailing list
discussion [0]. The details of the fix are in patch #1.

The main idea for the fix belongs to Yonghong Song,
mine contribution is merely in review and test cases.

There are some changes in verification performance:

File                       Program        Insns    (DIFF)  States  (DIFF)
-------------------------  -------------  ---------------  --------------
pyperf600_bpf_loop.bpf.o   on_event          +15 (+0.42%)     +0 (+0.00%)
strobemeta_bpf_loop.bpf.o  on_event        +857 (+37.95%)   +60 (+38.96%)
xdp_synproxy_kern.bpf.o    syncookie_tc   +2892 (+30.39%)  +109 (+36.33%)
xdp_synproxy_kern.bpf.o    syncookie_xdp  +2892 (+30.01%)  +109 (+36.09%)

(when tested on a subset of selftests identified by
 selftests/bpf/veristat.cfg and Cilium bpf object files from [4])

Changelog:
v2 [2] -> v3:
- fixes for verifier.c commit message as suggested by Yonghong;
- patch-set re-rerouted to 'bpf' tree as suggested in [2];
- patch for test_tcp_custom_syncookie is sent separately to 'bpf-next' [3].
- veristat results updated using 'bpf' tree as baseline and clang 16.

v1 [1] -> v2:
- patch #2 commit message updated to better reflect verifier behavior
  with regards to checkpoints tree (suggested by Yonghong);
- veristat results added (suggested by Andrii).

[0] https://lore.kernel.org/bpf/9b251840-7cb8-4d17-bd23-1fc8071d8eef@linux.dev/
[1] https://lore.kernel.org/bpf/20240212143832.28838-1-eddyz87@gmail.com/
[2] https://lore.kernel.org/bpf/20240216150334.31937-1-eddyz87@gmail.com/
[3] https://lore.kernel.org/bpf/20240222150300.14909-1-eddyz87@gmail.com/
[4] https://github.com/anakryiko/cilium
====================

Link: https://lore.kernel.org/r/20240222154121.6991-1-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>