add official way to dump network tracing info

just uncomment the specific node in app.config, no need to recompile
to take effect. It will be shipped as Shadowsocks.exe.config after built.

This is for debugging only.

shadowsocks-csharp/app.config

@@ -39,4 +39,49 @@
       </setting>
     </Shadowsocks.Properties.Settings>
   </userSettings>
+  <!--
+    <system.diagnostics>
+    <sources>
+      <source name="System.Net" tracemode="includehex" maxdatasize="1024">
+        <listeners>
+          <add name="System.Net"/>
+        </listeners>
+      </source>
+      <source name="System.Net.Cache">
+        <listeners>
+          <add name="System.Net"/>
+        </listeners>
+      </source>
+      <source name="System.Net.Http">
+        <listeners>
+          <add name="System.Net"/>
+        </listeners>
+      </source>
+      <source name="System.Net.Sockets">
+        <listeners>
+          <add name="System.Net"/>
+        </listeners>
+      </source>
+      <source name="System.Net.WebSockets">
+        <listeners>
+          <add name="System.Net"/>
+        </listeners>
+      </source>
+    </sources>
+    <switches>
+      <add name="System.Net" value="Verbose"/>
+      <add name="System.Net.Cache" value="Verbose"/>
+      <add name="System.Net.Http" value="Verbose"/>
+      <add name="System.Net.Sockets" value="Verbose"/>
+      <add name="System.Net.WebSockets" value="Verbose"/>
+    </switches>
+    <sharedListeners>
+      <add name="System.Net"
+        type="System.Diagnostics.TextWriterTraceListener"
+        initializeData="network-tracing.log"
+      />
+    </sharedListeners>
+    <trace autoflush="true"/>
+  </system.diagnostics>
+  -->
 </configuration>