dnsdist: setServFailWhenNoServer mirrors EDNS options and query flags

[Habbie]

• Program: dnsdist
• Issue type: Bug report

Short description

Like #6847 / #6348 but for setServFailWhenNoServer(true)

Environment

• Operating system:
• Software version: I checked 1.5.1 and master

Steps to reproduce

1. start dnsdist with no (up) backends
2. setServFailWhenNoServer(true)
3. issue a query with EDNS options (+cookie +nsid)

Expected behaviour

SERVFAIL response with EDNS but without cookie, empty NSID, and my AD flag.

Actual behaviour

; <<>> DiG 9.11.5-P4-5.1+deb10u2-Debian <<>> a example.com @127.0.0.1 -p 5300 +nsid
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 44564
;; flags: qr rd ad; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1
;; WARNING: recursion requested but not available

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
; NSID
; COOKIE: 935507bf57bc90ae (echoed)
;; QUESTION SECTION:
;example.com.			IN	A

;; Query time: 0 msec
;; SERVER: 127.0.0.1#5300(127.0.0.1)
;; WHEN: Mon Jan 25 14:10:49 CET 2021
;; MSG SIZE  rcvd: 56

Other information

Perhaps the bufsize should also not be mirrored from the query.