dnsdist: Handle HTTP/3 errors, refactor QUIC regression tests

[rgacogne]

Short description

Checklist

I have:

• read the CONTRIBUTING.md document
• compiled this code
• tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)
• checked that this code was merged to master

[coveralls]

Pull Request Test Coverage Report for Build 6970480146

Warning: This coverage report may be inaccurate.

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A quick fix for this PR: rebase it; your next report should be accurate.

• 8 of 10 (80.0%) changed or added relevant lines in 1 file are covered.
• 28 unchanged lines in 6 files lost coverage.
• Overall coverage increased (+0.03%) to 57.444%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pdns/dnsdistdist/doh3.cc	8	10	80.0%

Files with Coverage Reduction	New Missed Lines	%
pdns/sodcrypto.cc	1	90.51%
pdns/misc.cc	2	62.96%
pdns/dnsdist-carbon.cc	3	57.29%
pdns/iputils.cc	4	44.17%
pdns/packethandler.cc	5	72.98%
pdns/recursordist/test-syncres_cc1.cc	13	88.95%

Totals
Change from base Build 6958137169:	0.03%
Covered Lines:	106095
Relevant Lines:	154037

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💛 - Coveralls