AP_REQ verification impossible for supplied netbios names

[bolkedebruin]

Microsoft clients can request tickets with their Netbios names which are typically net resolvable in a non AD context. In the case that the address list only contains NetBIOS addresses MIT Kerberos treats these lists as empty see:

https://github.com/krb5/krb5/blob/34625d594c339a077899fa01fc4b5c331a1647d0/src/lib/krb5/krb/addr_srch.c#L48

I suggest doing the same and will provide a PR.