Sign and verify PAC with ticket principal instead of canon principal

Sign and verify PAC with ticket principal instead of canon principal

With MIT library 1.18 the KDC no longer set
KRB5_KDB_FLAG_CANONICALIZE for enterprise principals which allows
us to not canonicalize them (like in Windows / Heimdal).

However, it now breaks the PAC signature verification as it was
wrongly done using canonical client rather than ticket client name.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14342

Signed-off-by: Isaac Boukris <iboukris@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>
Reviewed-by: Guenther Deschner <gd@samba.org>