Revert "sched: Remove extra put_online_cpus() inside sched_setaffinity()"

This reverts commit 7f2cd15acbae57ff17eb4e3bf34cc37a5b5e148f.
Revert "sched: Fix select_idle_sibling() bouncing cow syndrome"

This reverts commit f3ebe75a23ac94e78815687df98b60246c58757c.