rec: Backport 14628 to rec 5.1.x: rec: avoid duplicated waiter ids for chained requests

[omoerbeek]

Short description

Backport of #14628

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 11347194459

Details

• 5 of 5 (100.0%) changed or added relevant lines in 2 files are covered.
• 73 unchanged lines in 7 files lost coverage.
• Overall coverage decreased (-0.06%) to 66.34%

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Files with Coverage Reduction	New Missed Lines	%
pdns/recursordist/test-syncres_cc2.cc	3	88.85%
pdns/remote_logger.cc	3	52.68%
pdns/iputils.cc	6	33.95%
pdns/recursordist/rec-tcpout.cc	6	50.79%
pdns/recursordist/syncres.cc	10	79.57%
pdns/recursordist/taskqueue.cc	11	34.15%
pdns/recursordist/rec-taskqueue.cc	34	40.14%

Totals
Change from base Build 11161224661:	-0.06%
Covered Lines:	56857
Relevant Lines:	75723

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💛 - Coveralls