dnsdist: Document dnsdist_ffi_stat_node_get_children_* return children+node stats

[rgacogne]

Short description

The dnsdist_ffi_stat_node_get_children_* methods return the sum of the queries or responses received for the children of a node AND the node itself. It's quite unexpected but breaking the existing behaviour now would be painful.

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 12765583697

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 24 unchanged lines in 9 files lost coverage.
• Overall coverage decreased (-9.2%) to 64.916%

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Files with Coverage Reduction	New Missed Lines	%
pdns/packethandler.cc	1	72.44%
modules/gpgsqlbackend/gpgsqlbackend.cc	1	88.62%
pdns/recursordist/recursor_cache.cc	1	84.42%
modules/lmdbbackend/lmdbbackend.cc	2	73.74%
pdns/rcpgenerator.cc	2	90.55%
pdns/misc.hh	3	87.62%
pdns/misc.cc	4	64.68%
pdns/recursordist/syncres.cc	5	80.04%
pdns/signingpipe.cc	5	83.38%

Totals
Change from base Build 12765482410:	-9.2%
Covered Lines:	126368
Relevant Lines:	163844

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💛 - Coveralls