Comment 7 for bug 1731522

According to https://github.com/systemd/systemd/issues/6520 this can be worked around by setting DNSStubListener=yes in /etc/systemd/resolved.conf. This is disabled by default due to <https://github.com/systemd/systemd/pull/4061>.

It is not ideal to have systemd-resolved conflict with other nameservers listening on 0.0.0.0:53, but as a default behavior of systemd-resolved in Ubuntu, barring any other upstream fix for <https://github.com/systemd/systemd/issues/6520>, this should be our fallback position for bionic.