This is also fixed in network-manager upstream (git://git.freedesktop.org/git/NetworkManager/NetworkManager.git) by commit d1295b12e9f802867edef57ee02c87495df1683e ("dhcp: wait for an IPv6LL address before starting DHCPv6 (bgo #740147)") which is included in Ubuntu network-manager starting in wily.
This is also fixed in network-manager upstream (git:// git.freedesktop .org/git/ NetworkManager/ NetworkManager. git) by commit d1295b12e9f8028 67edef57ee02c87 495df1683e ("dhcp: wait for an IPv6LL address before starting DHCPv6 (bgo #740147)") which is included in Ubuntu network-manager starting in wily.