Warn on out-of-order or duplicated packets (or missing nonce increment!)

src/network/networktransport.h

@@ -104,6 +104,7 @@ namespace Network {
     const struct in_addr & get_remote_ip( void ) const { return connection.get_remote_ip(); }
 
     const NetworkException *get_send_exception( void ) const { return connection.get_send_exception(); }
+    const NetworkException *get_recv_exception( void ) const { return connection.get_recv_exception(); }
   };
 }