base-files: properly generate the ula

Signed-off-by: John Crispin <blogic@openwrt.org>

SVN-Revision: 42261

package/base-files/files/bin/config_generate

@@ -16,7 +16,7 @@ set network.loopback.ipaddr='127.0.0.1'
 set network.loopback.netmask='255.0.0.0'
 delete network.globals
 set network.globals='globals'
-set network.globals.ula_prefix='fdb1:a57f:2544::/48'
+set network.globals.ula_prefix='auto'
 EOF
 }