Change xfer-out timer message log level to DEBUG(1)

When max-transfer-*-out timeouts were reintroduced, the log message
about starting the timer was errorneously left as ISC_LOG_ERROR.
Change the log level of said message to ISC_LOG_DEBUG(1).

lib/ns/xfrout.c

@@ -1155,7 +1155,7 @@ have_stream:
 
 	/* Start the timers */
 	if (xfr->maxtime > 0) {
-		xfrout_log(xfr, ISC_LOG_ERROR,
+		xfrout_log(xfr, ISC_LOG_DEBUG(1),
 			   "starting maxtime timer %" PRIu64 " ms",
 			   xfr->maxtime);
 		isc_nm_timer_start(xfr->maxtime_timer, xfr->maxtime);