netifd: pass on delegate flag from dhcp to 6rd

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@39909 3c298f89-4303-0410-b956-a3cf2f4a3e73
odhcp6c: pass on delegate-flag on to ds-lite interface

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@39910 3c298f89-4303-0410-b956-a3cf2f4a3e73