dnsdist: Add ChangeLog and secpoll entry for DNSdist 1.9.8

[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)

[coveralls]

Pull Request Test Coverage Report for Build 12373378557

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 51 unchanged lines in 13 files lost coverage.
• Overall coverage decreased (-0.008%) to 64.823%

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Files with Coverage Reduction	New Missed Lines	%
modules/gpgsqlbackend/gpgsqlbackend.cc	1	88.62%
pdns/dnsdistdist/dnsdist-backend.cc	1	66.73%
pdns/recursordist/aggressive_nsec.cc	2	66.17%
pdns/sstuff.hh	2	56.83%
pdns/dnsdistdist/dnsdist.cc	2	68.85%
pdns/stubresolver.cc	3	77.58%
pdns/recursordist/syncres.cc	3	80.29%
pdns/opensslsigners.cc	3	61.34%
pdns/recursordist/recpacketcache.hh	3	89.55%
pdns/iputils.hh	3	78.25%

Totals
Change from base Build 12372290513:	-0.008%
Covered Lines:	126114
Relevant Lines:	163764

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💛 - Coveralls

[rgacogne]

Applied Peter's suggestions, and rebased on master.