sched/core: Add __always_inline to schedule_loop()

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2232098

Upstream Status: RHEL only

Without __always_inline, this function breaks wchan.

schedule_loop() was added by patches from the upstream RT tree; a respin of the patches for upstream has __always_inline.

Signed-off-by: Crystal Wood swood@redhat.com