EPN: Don't downgrade security
If an administrator requests `smtp_security=starttls`, but SMTP
server disables STARTTLS, then EPN downgrade security to `none`,
which means plain text. Administrator doesn't expect such behavior.
Fixes: https://pagure.io/freeipa/issue/8578
Signed-off-by: Stanislav Levin <slev@altlinux.org>
Reviewed-By: Rob Crittenden <rcritten@redhat.com>
Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>