UPNP/NAT-PMP - add a handler for automatic port mapping provisioning
Add a handler for the provisioned port mappings (see #334 (closed) ). The handler must automatically maintain a pool of mapping ready for use whenever a call is started (outgoing/incoming). The handler must create new mappings if the number of available mappings drops under a pre-defined limit, and must also delete unnecessary mappings when the number of mapping exceeds a defined max limit.