CVE-2022-37966 kdc: Assume trust objects support AES by default

As part of matching the behaviour of Windows, assume that trust objects
support AES256, but not RC4, if not specified otherwise.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15219
BUG: https://bugzilla.samba.org/show_bug.cgi?id=15237

Signed-off-by: Joseph Sutton <josephsutton@catalyst.net.nz>
Reviewed-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
