VPN: silence VPN notifications.

Bug: 5852859
Change-Id: I269d8de298a1fd69a8d777150ae97927537a5424

Author: Chia-chi Yeh

services/java/com/android/server/connectivity/Vpn.java

@@ -322,7 +322,7 @@ private void showNotification(VpnConfig config, String label, Bitmap icon) {
                     .setContentTitle(title)
                     .setContentText(text)
                     .setContentIntent(VpnConfig.getIntentForStatusPanel(mContext, config))
-                    .setDefaults(Notification.DEFAULT_ALL)
+                    .setDefaults(0)
                     .setOngoing(true)
                     .getNotification();
             nm.notify(R.drawable.vpn_connected, notification);