auth dnsproxy: make local port range configurable

[zeha]

Short description

Address #13039 by making the local port range configurable.

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 10575397672

Details

• 10 of 16 (62.5%) changed or added relevant lines in 2 files are covered.
• 127 unchanged lines in 18 files lost coverage.
• Overall coverage decreased (-0.03%) to 64.662%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pdns/dnsproxy.cc	8	14	57.14%

Files with Coverage Reduction	New Missed Lines	%
pdns/backends/gsql/gsqlbackend.hh	1	97.71%
pdns/recursordist/test-syncres_cc2.cc	3	88.85%
pdns/misc.hh	3	87.62%
pdns/opensslsigners.cc	3	61.2%
pdns/recursordist/rec-main.cc	3	61.9%
pdns/rcpgenerator.cc	3	89.5%
pdns/misc.cc	3	63.94%
modules/gpgsqlbackend/spgsql.cc	3	67.94%
pdns/recursordist/test-syncres_cc1.cc	5	89.18%
pdns/dnsdistdist/dnsdist-tcp.cc	5	75.21%

Totals
Change from base Build 10575147394:	-0.03%
Covered Lines:	124622
Relevant Lines:	162055

---

💛 - Coveralls