Feature Request: Option for EDNS Client Subnet (RFC7871)

[DarkDeviL]

Some authoritative DNS servers give different responses depending on the Client IP and/or EDNS Client Subnet (RFC7871), as such, it would be nice with an option to set a custom EDNS Client Subnet to send through with the DNS queries.

Google's DNS over HTTPS already provides a such option, named "edns_client_sunbet", which is a true copy of what I'm suggesting.

The default (if unset/empty) should of course still stay with the current way, where it does not include anything.