sched: Export sched_setscheduler_nocheck

The new locktorture rtmutex_lock tests exercise priority boosting, which
means that they need to set some tasks to real-time priority.  To do this,
they use sched_setscheduler_nocheck().  However, this is not exported to
modules, which results in the following error when building locktorture
as a module:

ERROR: "sched_setscheduler_nocheck" [kernel/locking/locktorture.ko] undefined!

This commit therefore adds an EXPORT_SYMBOL_GPL() to allow this function
to be invoked from locktorture when built as a module.
Reported-by: NStephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: NDavidlohr Bueso <dave@stgolabs.net>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: NIngo Molnar <mingo@kernel.org>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>

kernel/sched/core.c

@@ -4022,6 +4022,7 @@ int sched_setscheduler_nocheck(struct task_struct *p, int policy,
 {
 	return _sched_setscheduler(p, policy, param, false);
 }
+EXPORT_SYMBOL_GPL(sched_setscheduler_nocheck);
 
 static int
 do_sched_setscheduler(pid_t pid, int policy, struct sched_param __user *param)