db-glue.c: set forwardable flag on cross-realm tgt tickets

db-glue.c: set forwardable flag on cross-realm tgt tickets

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14233

Match Windows behavior and allow the forwardable flag to be
set in cross-realm tickets. We used to allow forwardable to
any server, but now that we apply disallow-forwardable policy
in heimdal we need to explicitly allow in the corss-realm case
(and remove the workaround we have for it the MIT plugin).

Signed-off-by: Isaac Boukris <iboukris@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Autobuild-User(master): Andrew Bartlett <abartlet@samba.org>
Autobuild-Date(master): Fri Jun 12 22:10:34 UTC 2020 on sn-devel-184