Move InactivityCheck logic to private method.

src/net.h

@@ -338,6 +338,7 @@ private:
     void AcceptConnection(const ListenSocket& hListenSocket);
     void DisconnectNodes();
     void NotifyNumConnectionsChanged();
+    void InactivityCheck(CNode *pnode);
     void ThreadSocketHandler();
     void ThreadDNSAddressSeed();