Handle multiple UPnP WANDevice and WANConnection descriptions

Per Figure 1 of the InternetGatewayDevice specification
(http://upnp.org/specs/gw/UPnP-gw-InternetGatewayDevice-v1-Device.pdf),
an IGD may have multiple WAN devices, each with multiple WANConnection
services
Support for UPnP InternetGatewayDevice:2