Initialize all counters at startup

hark.go

@@ -48,6 +48,10 @@ func hark(ports []int, stopCh chan struct{}) error {
 		}
 		listeners = append(listeners, l)
 
+		// Reset the counter explicitly so the metrics appear even
+		// before the first connection.
+		connections.WithLabelValues(strconv.Itoa(port)).Add(0)
+
 		wg.Add(1)
 		go func(port int) {
 			listener(l, port)