fix timer_test: don't forget to set tv_usec on the stop time

The timer_test schedules timers and records the desired stop time. Also store
the usec value of the desired stop time, because scheduling at e.g. sec N usec
999999 but recording sec N usec 0, and then receiving a timer at sec N+1 usec 0
is only 1 usec late, but records as 1000000 usecs late. This might have been
the main cause of the timer test not working well on the osmocom build server.

Change-Id: I13bb60f7d341a397f95d13d9c63c40188b6cd5a0

tests/timer/timer_test.c

@@ -95,6 +95,7 @@ static void main_timer_fired(void *data)
 		v->timer.data = v;
 		unsigned int seconds = (random() % 10) + 1;
 		v->stop.tv_sec = v->start.tv_sec + seconds;
+		v->stop.tv_usec = v->start.tv_usec;
 		osmo_timer_schedule(&v->timer, seconds, 0);
 		llist_add(&v->head, &timer_test_list);
 	}