PR description:
> Following up on the BIP155 addrv2 changes, and starting with core#19845, RPC getnetworkinfo began returning networks with empty names.
>
> This patch:
>
> - updates `GetNetworkName()` to the current Network enum
> - updates `getNetworksInfo()` to ignore as-yet unsupported networks
> - adds regression tests
This is a backport of core#20120