optimize receive file

src/main/base/org/bdware/sc/ContractPort.java

@@ -111,7 +111,7 @@ public class ContractPort {
         KeyValueDBUtil.instance.setValue(CMTables.ContractInfo.toString(), USED_PORTS, JsonUtil.toJson(usedPorts));
     }
 
-    interface PortVisitor {
+    public interface PortVisitor {
         /**
          * check if the port is listened
          *