use efficient net by default

source/network/XNet.cpp

@@ -55,7 +55,7 @@ void XNetClearAll()
 XNet::XNet()
 XNet::XNet()
 {
 {
     nodes.Clear();
     nodes.Clear();
-    isGradEfficient = false;
+    isGradEfficient = true;
 }
 }
 
 
 /* de-constructor */
 /* de-constructor */