flip the client-to-server port mapping

The port that the client requests should be mapped to the port
where the server is listening, not the other way around.

fixes #29

onionperf/measurement.py

@@ -208,7 +208,7 @@ def run(self, do_onion=True, do_inet=True, client_tgen_listen_port=58888, client
                 general_writables.append(self.__start_tgen_server(server_tgen_listen_port))
 
             if do_onion:
-                tor_writable, torctl_writable = self.__start_tor_server(server_tor_ctl_port, server_tor_socks_port, {server_tgen_listen_port:client_tgen_connect_port})
+                tor_writable, torctl_writable = self.__start_tor_server(server_tor_ctl_port, server_tor_socks_port, {client_tgen_connect_port:server_tgen_listen_port})
                 general_writables.append(tor_writable)
                 general_writables.append(torctl_writable)