Set the dns message id to 0 for doh requests

[VanStratum]

The doh rfc says in section 4.1 that the dns messages ids should be set to 0 to be more cache friendly. This could be useful when testing caching doh servers, or servers behind a http cache.

This would however necessitate changing the message tracking method.

[weyrick]

Interesting, ok perhaps we could switch to an internal id for tracking, based on a quick hash of some properties in the message.

[VanStratum]

I ran in a similar issue with DoQ, where the stream id identifies the request.