finish tcp rendezvous keep alive logic following mqtt, but defined by

server so that it can be easily to be controlled at server side.

src/common.rs

@@ -1278,7 +1278,7 @@ pub async fn secure_tcp(conn: &mut FramedStream, key: &str) -> ResultType<()> {
                         });
                         timeout(CONNECT_TIMEOUT, conn.send(&msg_out)).await??;
                         conn.set_key(key);
-                        log::info!("Token secured");
+                        log::info!("Connection secured");
                     }
                     _ => {}
                 }