ipipe: timer: resume hardware operations in oneshot handler

Although we won't allow disabling the hardware when the clock event
logic switches a device to stopped mode - so that we won't affect the
timer logic running on the head stage unexpectedly -, we still have to
enable the hardware when switched (back) to oneshot mode, since it may
have been stopped prior to interposing on the device in
ipipe_timer_start().

Failing to do so would leave the hardware shut down for both regular
and Xenomai operations, with no mean to bring it up again.

kernel/ipipe/timer.c

@@ -364,6 +364,7 @@ static int do_set_oneshot(struct clock_event_device *cdev)
 {
 	struct ipipe_timer *timer = __ipipe_raw_cpu_read(percpu_timer);
 
+	timer->orig_set_state_oneshot(cdev);
 	timer->mode_handler(CLOCK_EVT_MODE_ONESHOT, cdev);
 
 	return 0;