CVE-2022-32744 s4:kdc: Don't allow HDB keytab iteration

CVE-2022-32744 s4:kdc: Don't allow HDB keytab iteration

A fallback in krb5_rd_req_ctx() means that Samba's kpasswd service will
try many inappropriate keys to decrypt the ticket supplied to it. For
example, it will accept a ticket encrypted with the Administrator's key,
when it should rather accept only tickets encrypted with the krbtgt's
key (and not an RODC krbtgt). To fix this, declare the HDB keytab using
the HDBGET ops, which do not support iteration.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15074

Signed-off-by: Joseph Sutton <josephsutton@catalyst.net.nz>
Reviewed-by: Andreas Schneider <asn@samba.org>