Explicitly set defaults for service notifications

app/src/main/java/eu/faircode/email/ServiceExternal.java

@@ -141,6 +141,7 @@ public class ServiceExternal extends Service {
                         .setContentTitle(getString(R.string.tile_synchronize))
                         .setAutoCancel(false)
                         .setShowWhen(false)
+                        .setDefaults(0) // disable sound on pre Android 8
                         .setPriority(NotificationCompat.PRIORITY_MIN)
                         .setCategory(NotificationCompat.CATEGORY_SERVICE)
                         .setVisibility(NotificationCompat.VISIBILITY_SECRET)

app/src/main/java/eu/faircode/email/ServiceSend.java

@@ -174,6 +174,7 @@ public class ServiceSend extends ServiceBase {
                         .setContentIntent(pi)
                         .setAutoCancel(false)
                         .setShowWhen(true)
+                        .setDefaults(0) // disable sound on pre Android 8
                         .setLocalOnly(true)
                         .setPriority(NotificationCompat.PRIORITY_MIN)
                         .setCategory(NotificationCompat.CATEGORY_SERVICE)

app/src/main/java/eu/faircode/email/ServiceSynchronize.java

@@ -717,6 +717,7 @@ public class ServiceSynchronize extends ServiceBase implements SharedPreferences
                         .setAutoCancel(false)
                         .setShowWhen(false)
                         .setPriority(NotificationCompat.PRIORITY_MIN)
+                        .setDefaults(0) // disable sound on pre Android 8
                         .setCategory(NotificationCompat.CATEGORY_SERVICE)
                         .setVisibility(NotificationCompat.VISIBILITY_SECRET)
                         .setLocalOnly(true);