reduce frame send time too slow to a warning instead of error

src/zm_monitorstream.cpp

@@ -425,7 +425,7 @@ bool MonitorStream::sendFrame(Image *image, struct timeval *timestamp) {
     int frameSendTime = tvDiffMsec( frameStartTime, frameEndTime );
     if ( frameSendTime > 1000/maxfps ) {
       maxfps /= 1.5;
-      Error( "Frame send time %d msec too slow, throttling maxfps to %.2f", frameSendTime, maxfps );
+      Warning("Frame send time %d msec too slow, throttling maxfps to %.2f", frameSendTime, maxfps);
     }
   }
   last_frame_sent = TV_2_FLOAT( now );