Merge branch 'bpf-add-a-generic-bits-iterator'

Yafang Shao says:

====================
bpf: Add a generic bits iterator

Three new kfuncs, namely bpf_iter_bits_{new,next,destroy}, have been
added for the new bpf_iter_bits functionality. These kfuncs enable the
iteration of the bits from a given address and a given number of bits.

- bpf_iter_bits_new
  Initialize a new bits iterator for a given memory area. Due to the
  limitation of bpf memalloc, the max number of bits to be iterated
  over is (4096 * 8).
- bpf_iter_bits_next
  Get the next bit in a bpf_iter_bits
- bpf_iter_bits_destroy
  Destroy a bpf_iter_bits

The bits iterator can be used in any context and on any address.

Changes:
- v7->v8:
  Refine the interface to avoid dealing with endianness (Andrii)
- v6->v7:
  Fix endianness error for non-long-aligned data (Andrii)
- v5->v6:
  Add positive tests (Andrii)
- v4->v5:
  Simplify test cases (Andrii)
- v3->v4:
  - Fix endianness error on s390x (Andrii)
  - zero-initialize kit->bits_copy and zero out nr_bits (Andrii)
- v2->v3:
  Optimization for u64/u32 mask (Andrii)
- v1->v2:
  Simplify the CPU number verification code to avoid the failure on s390x
  (Eduard)
- bpf: Add bpf_iter_cpumask
  https://lwn.net/Articles/961104/
- bpf: Add new bpf helper bpf_for_each_cpu
  https://lwn.net/Articles/939939/
====================

Link: https://lore.kernel.org/r/20240517023034.48138-1-laoar.shao@gmail.com
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>