The `nat-local` and `nat-remote` keys contain information on the NAT
status of the local and remote IKE endpoints, respectively. If a
responder did not detect a NAT but is configured to fake a NAT situation
this is indicated by `nat-fake` (if an initiator fakes a NAT situation
`nat-local` is set). If any NAT is detected or faked `nat-any` is set.
Closesstrongswan/strongswan#16.