Merge branch 'Allow bpf_user_ringbuf_drain() callbacks to return 1'

David Vernet says:

====================
The bpf_user_ringbuf_drain() helper function allows a BPF program to
specify a callback that is invoked when draining entries from a
BPF_MAP_TYPE_USER_RINGBUF ring buffer map. The API is meant to allow the
callback to return 0 if it wants to continue draining samples, and 1 if
it's done draining. Unfortunately, bpf_user_ringbuf_drain() landed shortly
after commit 1bfe26fb0827 ("bpf: Add verifier support for custom
callback return range"), which changed the default behavior of callbacks
to only support returning 0, and the corresponding necessary change to
bpf_user_ringbuf_drain() callbacks was missed.

This patch set fixes this oversight, and updates the user_ringbuf
selftests to return 1 in a callback to catch future instances of
regression.
====================

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>