Rearranged code and changed Curl_readwrite_init() and Curl_pre_readwrite() into

do_init() and do_complete() which now are called first and last in the DO
function. It simplified the flow in multi.c and the functions got more
sensible names!

lib/tftp.c

@@ -725,10 +725,6 @@ static CURLcode Curl_tftp(struct connectdata *conn, bool *done)
   }
   state = (tftp_state_data_t *)data->reqdata.proto.tftp;
 
-  code = Curl_readwrite_init(conn);
-  if(code)
-    return code;
-
   /* Run the TFTP State Machine */
   for(code=tftp_state_machine(state, TFTP_EVENT_INIT);
       (state->state != TFTP_STATE_FIN) && (code == CURLE_OK);