OPT PSEUDOSECTION: EDNS udp buffer always 4096

Example query sample directed at `8.8.8.8`:

```
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
```

Example query sample directed at a local `dnsproxy` instance:

```
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
```

I had expected, perhaps incorrectly, that this was governed by `--udp-buf-size=`, but in testing it doesn't appear to be the case (chasing `--udp-buf-size=` around the code base it wasn't actually clear to me where/if this value is/was used at all, but that's very likely my fault).

Possible bug, probable misunderstanding and/or `PEBCAK`.