Configure user data for ipv6 in PDC

The config we want is: [connection] ipv6.addr-gen-mode=0

ref https://gitlab.cern.ch/kubernetes/project/-/issues/758

ref https://gitlab.cern.ch/kubernetes/automation/releases/kops-openstack/-/issues/71

Signed-off-by: Spyros Trigazis spyridon.trigazis@cern.ch