6relayd: compatibility with broken IPv6 devices
* Announce ULA as deprecated if other addresses are available
* Allow the announced DNS-server to be overwritten

git-svn-id: svn://svn.openwrt.org/openwrt@35803 3c298f89-4303-0410-b956-a3cf2f4a3e73
6relayd: Fix config behaviour for rewrite_dns_addr option

git-svn-id: svn://svn.openwrt.org/openwrt@35804 3c298f89-4303-0410-b956-a3cf2f4a3e73