Fix UPnP IGD search and port mapping deletion

[sauwming]

It is reported that freeing the XML document returned by UpnpActionComplete_get_ActionResult() will cause crash.

Note that I am unable to reproduce the issue on my Mac (even under Address Sanitizer), but according to the sample:
https://github.com/pupnp/pupnp/blob/branch-1.14.x/upnp/sample/common/sample_util.c#L447
it seems to be unnecessary to call ixmlDocument_free().

Another fix in this PR is to remove the version matching for the IGD.

 * Devices specified by UPnP vendors, must begin with urn:,
 * followed by an ICANN domain name owned by the vendor, followed by :device:,
 * followed by a device type suffix, colon, and an integer version, i.e.,
 * urn:domain-name:device:deviceType:v.

In my newest router device, it broadcasts that it uses version 2: urn:schemas-upnp-org:device:InternetGatewayDevice:2.