AA: base-files: merge new sysctl-behaviour from trunk

git-svn-id: svn://svn.openwrt.org/openwrt@36732 3c298f89-4303-0410-b956-a3cf2f4a3e73
AA: netifd: remove deprecated IPv6 sysctls

git-svn-id: svn://svn.openwrt.org/openwrt@36733 3c298f89-4303-0410-b956-a3cf2f4a3e73
AA: Update ipv6-support migration path

git-svn-id: svn://svn.openwrt.org/openwrt@36734 3c298f89-4303-0410-b956-a3cf2f4a3e73
AA: ipv6-support: align default ip6assign with trunk

git-svn-id: svn://svn.openwrt.org/openwrt@36735 3c298f89-4303-0410-b956-a3cf2f4a3e73