This static method returns a NetworkCapabilities instance with
transports and capabilities set according to the given legacy type.
Also:
- add NetworkRequest.Builder.setCapabilities(), to be able to use
the NetworkCapabilities instances returned from the above
- update UpstreamNetworkMonitor to make immediate use of this
Test: as follows
- build (bullhead)
- flashed
- booted
- runtest frameworks-net passes
- WiFi to DUN upstream tethering works
Bug: 32163131
Change-Id: Idfe1ddd2815c355cbf27cf29eb0e3de177de84e9