odhcp6c: don't assign addresses or prefixes prematurely

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@42850 3c298f89-4303-0410-b956-a3cf2f4a3e73
odhcp6c: fix typo in last commit

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@42852 3c298f89-4303-0410-b956-a3cf2f4a3e73