Use gUPnP-igd to implement add/remove port mappings
Review Request #1789 — Created Sept. 18, 2022 and submitted
Unfortunately, there appears to be no way to cancel a mapping request, so I've removed that function, and removed the return values used for cancelling. If cancelling comes back, it'll probably be in the form of a
We removed implicit automatic port mapping when we replaced
giocode. Protocols should probably be explicit about when they request a port mapping, but they haven't been made to do that yet.