Return START_STICKY from onStartCommand()

The _FLAG_ variant is the input enum, replace it
with the value-equivalent properly typed enum.

core/src/main/java/de/danoeh/antennapod/core/service/GpodnetSyncService.java

@@ -83,7 +83,7 @@ public class GpodnetSyncService extends Service {
         } else {
             Log.e(TAG, "Received invalid intent: action argument is null");
         }
-        return START_FLAG_REDELIVERY;
+        return START_STICKY;
     }
 
     @Override