Merge branch 'bpf-kernel-bpf-task_iter-c-don-t-abuse-next_thread'

Oleg Nesterov says:

====================
bpf: kernel/bpf/task_iter.c: don't abuse next_thread()

Compile tested.

Every lockless usage of next_thread() was wrong, bpf/task_iter.c is
the last user and is no exception.

====================

Link: https://lore.kernel.org/r/20231114163211.GA874@redhat.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>