Reduce default network flush time

The dump1090 network outputs don't offer timing guarantees or real-time
timestamps, but it is still useful for aggregators to locally timestamp
messages they receive from dump1090 on a best-effort basis.
With lower message rates, 500 ms of flush interval can result in
significant jitter for those timestamps.
Most installs send data only on the local network or non-metered
internet connections.
If necessary this default can be adjusted via --net-ro-interval by users
who require a longer flush interval for some reason.

Reduce the default flush time to 90 ms to reliably flush every 2nd
demodulation buffer when talking to an SDR (50 ms loop) and every loop
iteration when running network-only (100 ms loop).

fixes: flightaware#244

dump1090.c

@@ -122,7 +122,7 @@ static void modesInitConfig(void) {
 
     Modes.net_heartbeat_interval = MODES_NET_HEARTBEAT_INTERVAL;
     Modes.net_output_flush_size = 1300;
-    Modes.net_output_flush_interval = 500;
+    Modes.net_output_flush_interval = 90;
 
     // adaptive
     Modes.adaptive_min_gain_db = 0;