add subnet to StackAsync and add test for local arp resolving

arp/handler.go

@@ -51,7 +51,7 @@ func (h *Handler) Reset(cfg HandlerConfig) error {
 		return errors.New("invalid Handler query or pending config")
 	}
 	*h = Handler{
-		connID:          h.connID,
+		connID:          h.connID + 1,
 		ourHWAddr:       h.ourHWAddr[:0],
 		ourProtoAddr:    h.ourProtoAddr[:0],
 		htype:           cfg.HardwareType,