Merge branch 'libbpf-api-to-partially-consume-items-from-ringbuffer'

Andrea Righi says:

====================
libbpf: API to partially consume items from ringbuffer

Introduce ring__consume_n() and ring_buffer__consume_n() API to
partially consume items from one (or more) ringbuffer(s).

This can be useful, for example, to consume just a single item or when
we need to copy multiple items to a limited user-space buffer from the
ringbuffer callback.

Practical example (where this API can be used):
https://github.com/sched-ext/scx/blob/b7c06b9ed9f72cad83c31e39e9c4e2cfd8683a55/rust/scx_rustland_core/src/bpf.rs#L217

See also:
https://lore.kernel.org/lkml/20240310154726.734289-1-andrea.righi@canonical.com/T/#u

v4:
 - open a new 1.5.0 cycle

v3:
 - rename ring__consume_max() -> ring__consume_n() and
   ring_buffer__consume_max() -> ring_buffer__consume_n()
 - add new API to a new 1.5.0 cycle
 - fixed minor nits / comments

v2:
 - introduce a new API instead of changing the callback's retcode
   behavior
====================

Link: https://lore.kernel.org/r/20240406092005.92399-1-andrea.righi@canonical.com
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>