dnsdist: Handle response dnstap messages arriving before the query ones

[rgacogne]

Short description

Since we now use more than one TCP connection, it is entirely possible for the response message to arrive before the query one, and our tests should just deal with that.

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)

[coveralls]

Pull Request Test Coverage Report for Build 13368177434

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 541 unchanged lines in 20 files lost coverage.
• Overall coverage decreased (-0.09%) to 64.51%

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Files with Coverage Reduction	New Missed Lines	%
ext/lmdb-safe/lmdb-typed.hh	1	73.19%
modules/gpgsqlbackend/gpgsqlbackend.cc	1	88.62%
pdns/pollmplexer.cc	1	83.66%
pdns/recursordist/rec-web-stubs.hh	1	0.0%
pdns/arguments.cc	2	58.82%
pdns/tcpiohandler.cc	2	68.18%
pdns/misc.cc	3	62.79%
pdns/misc.hh	3	83.81%
pdns/rcpgenerator.cc	3	90.46%
pdns/dnsdistdist/dnsdist.cc	4	68.71%

Totals
Change from base Build 13326341755:	-0.09%
Covered Lines:	127634
Relevant Lines:	166873

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💛 - Coveralls