throttle: Add a way to know if throttle_schedule_timer had armed a timer.

This will be needed by the group throttling patches for the algorithm to be
accurate.

Signed-off-by: Benoit Canet <benoit@irqsave.net>
throttle: Add a way to fire one of the timers immediatly like a bottom half.

This will be needed by the group throttling algorithm.

Signed-off-by: Benoit Canet <benoit@irqsave.net>
throttle: Add throttle group support.

Signed-off-by: Benoit Canet <benoit@irqsave.net>