time-util: add and use USEC/NSEC_INFINIY

src/core/timer.c

@@ -46,8 +46,8 @@ static void timer_init(Unit *u) {
         assert(u);
         assert(u->load_state == UNIT_STUB);
 
-        t->next_elapse_monotonic_or_boottime = (usec_t) -1;
-        t->next_elapse_realtime = (usec_t) -1;
+        t->next_elapse_monotonic_or_boottime = USEC_INFINITY;
+        t->next_elapse_realtime = USEC_INFINITY;
         t->accuracy_usec = u->manager->default_timer_accuracy_usec;
 }