Utilising private EDE error codes to provide finer granularity to DNS UPDATE responses

[johanix]

• [x] Add support for private EDE codes to the code base
• [ ] Set a suitable EDE code on select error responses in parent (for delegation synchronization case).
• [ ] Set a suitable EDE code on select error responses in auth server (for updates to auth zone data).
• [x] Check for EDE messages in UPDATE responses and sore them in a suitable structure
• [ ] Present EDE data when relevant.

[johanix]

This mostly works fine. However there is presently a strange problem where adding an EDE in the failure path of zd.TrustUpdate(). This code (in tdns/updateresponder.go) works fine:

if zd.Options["frozen"] {
    log.Printf("UpdateResponder: zone %s is frozen (i.e. updates not possible). Ignoring update.",
        zd.ZoneName, qname)
    m.SetRcode(r, dns.RcodeRefused)
    AttachEDEToResponse(m, EDEZoneFrozen)
    w.WriteMsg(m)
    return nil
}

But this code (later in the same function) cause a FORMERR in the receiving client end:

err = zd.TrustUpdate(r, dur.Status)
if err != nil {
    zd.Logger.Printf("Error from TrustUpdate(): %v", err)
    m.SetRcode(m, int(dur.Status.ValidationRcode))
    AttachEDEToResponse(m, EDESig0KeyKnownButNotTrusted)
    w.WriteMsg(m)
    return err
}