Merge pull request #4611 from rgacogne/dnsdist-tcp-rfc7766-section10

dnsdist: Add TCP management options from rfc7766 section 10

diff --cc pdns/README-dnsdist.md
Simple merge

diff --cc pdns/dnsdist-lua.cc
Simple merge

diff --cc pdns/dnsdist-tcp.cc
Simple merge

diff --cc pdns/dnsdist.hh
Simple merge

diff --cc pdns/misc.cc
Simple merge

diff --cc pdns/misc.hh
Simple merge