Make cache-resolver respect EDNS

[ignoramous]

Cache resolver simply picks up a result from the cache and returns after modifying the query ID. It must also check if there are incoming EDNS opts if any, and reply as approp.

Example response with addn section as retrieved from cache, even when the client hadn't asked for it:

    "additionals": [
        {
            "name": ".",
            "type": "OPT",
            "udpPayloadSize": 4096,
            "extendedRcode": 0,
            "ednsVersion": 0,
            "flags": 0,
            "flag_do": false,
            "options": []
        }
    ]