rec: Backport Keytrap to rec-5.0.x

[omoerbeek]

Short description

Backport of #13781

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 7886140196

Details

• -96 of 820 (88.29%) changed or added relevant lines in 12 files are covered.
• 2178 unchanged lines in 36 files lost coverage.
• Overall coverage decreased (-2.4%) to 48.275%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pdns/recursordist/aggressive_nsec.cc	15	16	93.75%
pdns/recursordist/syncres.cc	11	13	84.62%
pdns/recursordist/test-syncres_cc.cc	20	22	90.91%
pdns/recursordist/rec-zonetocache.cc	3	8	37.5%
pdns/recursordist/rec-main.cc	0	7	0.0%
pdns/recursordist/test-syncres_cc4.cc	284	293	96.93%
pdns/recursordist/test-syncres_cc5.cc	110	124	88.71%
pdns/recursordist/pdns_recursor.cc	0	23	0.0%
pdns/validate.cc	103	136	75.74%

Files with Coverage Reduction	New Missed Lines	%
ext/yahttp/yahttp/router.hpp	1	0.0%
pdns/recursordist/rec_metrics.hh	2	0.0%
pdns/dnsname.hh	3	82.37%
pdns/epollmplexer.cc	3	75.3%
pdns/iputils.hh	3	58.13%
pdns/logger.hh	3	23.64%
pdns/recursordist/test-syncres_cc2.cc	3	88.99%
pdns/mplexer.hh	4	66.86%
pdns/recursordist/ext/luawrapper/include/LuaContext.hpp	5	2.97%
pdns/webserver.cc	5	0.0%

Totals
Change from base Build 7489736650:	-2.4%
Covered Lines:	41235
Relevant Lines:	72386

---

💛 - Coveralls