Change default forwarding method to optional on Yealink phones

Currently, when using Yealink phones there are two completely different methods of transferring depending on whether you would like to warm or cold transfer. By adding the line:
transfer.dsskey_deal_type=4
to the RingCentral Yealink provisioning server, phones will have an additional popup after trying to transfer a call asking if it will be direct or consult.