adsb_rx: enable RF amp by default on first run

firmware/application/external/adsbrx/ui_adsb_rx.cpp

@@ -542,6 +542,18 @@ ADSBRxView::ADSBRxView(NavigationView& nav) {
     logger = std::make_unique<ADSBLogger>();
     logger->append(logs_dir / u"ADSB.TXT");
 
+    /* First run only: start from the configuration that is known to receive
+     * ADS-B on this hardware -- LNA 32, VGA 32, RF amp ON. The first two are
+     * already ReceiverModel's defaults; the amp is not, and running without it
+     * costs about 14 dB, which is the difference between a busy list and an
+     * empty one. Once the user has saved settings for this app their choice
+     * wins, so this only sets the starting point.
+     * Going through the field rather than receiver_model keeps the displayed
+     * value in step: RFAmpField snapshots rf_amp() in its own constructor,
+     * which has already run by the time we get here. */
+    if (!settings_.loaded())
+        field_rf_amp.set_value(1);
+
     receiver_model.enable();
     baseband::set_adsb();