Fix IPv6 test_ns_connectivity #1653

Job	Run time
build-docker (internet.nl, docker/Dockerfile, app)	1m 59s
build-docker (unbound, docker/Dockerfile, unbound)	1m 5s
build-docker (linttest, docker/Dockerfile, linttest)	2m 41s
build-docker (test-runner, docker/test-runner.Dockerfile)	1m 7s
build-docker (webserver, docker/webserver.Dockerfile)	1m 9s
build-docker (grafana, docker/grafana.Dockerfile)	1m 20s
build-docker (util, docker/util.Dockerfile)	1m 21s
integration-test	3m 34s
docs	1s
lint/check	58s
test	2m 26s
batch-integration-test	2m 56s
development-environment-test	2m 30s
	23m 7s

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