s4:kdc: Don’t issue forwardable or proxiable tickets to Protected Users

s4:kdc: Don’t issue forwardable or proxiable tickets to Protected Users

If an authentication policy enforces a maximum TGT lifetime for a
Protected User, that limit should stand in place of the four-hour limit
usually applied to Protected Users; we should nevertheless continue to
ensure that forwardable or proxiable tickets are not issued to such
users.

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