torture: Add dowarn argument to torture_sched_setaffinity()

torture: Add dowarn argument to torture_sched_setaffinity()

Current use cases of torture_sched_setaffinity() are well served by its
unconditional warning on error.  However, an upcoming use case for a
preemption kthread needs to avoid warnings that might otherwise arise
when that kthread attempted to bind itself to a CPU on its way offline.
This commit therefore adds a dowarn argument that, when false, suppresses
the warning.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>