Dynamic DNS: List GWGs in Interface to send update from

Give the "Interface to send update from" field the same list as the "Interface to monitor" field, including gateway groups. When using most pre-coded Dynamic DNS providers that field is not displayed, and both these fields are set the same, so selecting a gateway group worked fine for those (99%) cases. But for users who want the "Custom" option, they could only select actual interfaces, not gateway groups.
Forum:  http://forum.pfsense.org/index.php/topic,70866.0.html