Enhancement Request: listen on a single port and split the authoritative & recursive queries using the RD flag

It would be nice to be able to make authoritative & recursive queries on a single port.

When getting a TLD's DS record(s) it is nice to be able to make an authoritative query so you know for sure the data returned has come from the blockchain itself. Authoritative dns querying is effectively a DNS API directly to the blockchain.

Both `bind` and `dnsdist` support splitting authoritative & recursive queries based on the RD flag, i.e. `RD=1` = recursive & `RD=0` = authoritative.

Seems to me this is a relative trivial change, tho i would imagine it should use a third port so the current functionality is retained.

The issue names no files or tests; start by locating the existing authoritative and recursive DNS listeners and how they inspect the RD flag. Determine how a single port and any additional port would preserve current behavior, then verify that RD=1 and RD=0 queries are routed as requested.

Written by the indexing model from the issue text.