fff-sysupgrade: install config via uci-defaults

Unfortunately the sysupgrade.conf is installed by base-files. The installed file
just contains examples and will be overwritten with this.

Signed-off-by: Tim Niemeyer <tim@tn-x.org>
Reviewed-by: Christian Dresel <fff@chrisi01.de>
Reviewed-by: Jan Kraus <mayosemmel@gmail.com>

src/packages/fff/fff-sysupgrade/files/etc/uci-defaults/99-fff-sysupgrade

@@ -1,6 +1,12 @@
+#!/bin/sh
+# Copyright 2017 Tim Niemeyer
+# License GPLv3
+
+cat > /etc/sysupgrade.conf <<-__EOF__
 /etc/shadow
 /etc/dropbear/dropbear_dss_host_key
 /etc/dropbear/dropbear_rsa_host_key
 /etc/dropbear/authorized_keys
 /etc/network.mode
 /etc/config/system
+__EOF__