Fix IPv6 test_ns_connectivity #1651

Job	Run time
build-docker (internet.nl, docker/Dockerfile, app)	2m 26s
build-docker (unbound, docker/Dockerfile, unbound)	1m 3s
build-docker (linttest, docker/Dockerfile, linttest)	4m 40s
build-docker (test-runner, docker/test-runner.Dockerfile)	4m 12s
build-docker (webserver, docker/webserver.Dockerfile)	1m 38s
build-docker (grafana, docker/grafana.Dockerfile)	1m 32s
build-docker (util, docker/util.Dockerfile)	1m 27s
docs	1s
test	3m 46s
lint/check	2m 38s
integration-test	5m 1s
development-environment-test	3m 40s
batch-integration-test	5m 24s
	37m 28s

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