Remove deprecated ip6slaac option
* use proto=dhcpv6 with reqprefix=no instead

git-svn-id: svn://svn.openwrt.org/openwrt@36280 3c298f89-4303-0410-b956-a3cf2f4a3e73
netifd: fix route / route6 regression (#13303)

git-svn-id: svn://svn.openwrt.org/openwrt@36281 3c298f89-4303-0410-b956-a3cf2f4a3e73