Enable native IPv6 support by default

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@36277 3c298f89-4303-0410-b956-a3cf2f4a3e73
Adapt default network configuration for IPv6

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@36278 3c298f89-4303-0410-b956-a3cf2f4a3e73