BUG/MEDIUM: checks: make sure to always apply offsets to now_ms in expiration

Now_ms can be zero nowadays, so it's not suitable for direct assignment to
t->expire, as there's a risk that the timer never wakes up once assigned
(TICK_ETERNITY). Let's use tick_add(now_ms, 0) for an immediate wakeup
instead. The impact here might be health checks suddenly stopping.

This should be backported where it applies.

Author: wtarreau

src/check.c

@@ -1279,7 +1279,7 @@ struct task *process_chk_conn(struct task *t, void *context, unsigned int state)
 		 * was erased during the bounce.
 		 */
 		if (!tick_isset(t->expire)) {
-			t->expire = now_ms;
+			t->expire = tick_add(now_ms, 0);
 			expired = 0;
 		}
 	}

src/extcheck.c

@@ -162,7 +162,7 @@ static void pid_list_expire(pid_t pid, int status)
 	HA_SPIN_LOCK(PID_LIST_LOCK, &pid_list_lock);
 	list_for_each_entry(elem, &pid_list, list) {
 		if (elem->pid == pid) {
-			elem->t->expire = now_ms;
+			elem->t->expire = tick_add(now_ms, 0);
 			elem->status = status;
 			elem->exited = 1;
 			task_wakeup(elem->t, TASK_WOKEN_IO);