base-files: remove IPv6-forwarding setting for all interfaces

git-svn-id: svn://svn.openwrt.org/openwrt@35344 3c298f89-4303-0410-b956-a3cf2f4a3e73
odhcp6c: work-around for proto-script to avoid loosing the default route

git-svn-id: svn://svn.openwrt.org/openwrt@35345 3c298f89-4303-0410-b956-a3cf2f4a3e73
netifd: add SLAAC ipv6 value for static-proto

git-svn-id: svn://svn.openwrt.org/openwrt@35346 3c298f89-4303-0410-b956-a3cf2f4a3e73