Merge pull request #10489 from slowr/ixfr-axfr-aware

dnsdist: Make DNSDist XFR aware when transfer is finished

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

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

diff --cc pdns/dnsdistdist/dnsdist-tcp-upstream.hh
Simple merge

diff --cc pdns/dnsdistdist/test-dnsdisttcp_cc.cc
Simple merge