[th/resolvconf-witten-no-workaround] ipv4: tighten up check for nameserver in @ipv4_dns_resolvconf_symlinked,@ipv4_dns_resolvconf_file

This effectively reverts commit 1a5da593 ('ipv4: dns: wait for nameserver to be wriitten').

Back then, the workaround was necessary due to rh#1778798. I can no longer reproduce that old issue, so presumably it was fixed.

Drop the workaround (by setting the wait-time to zero).

Note that this also re-enables the test for older NetworkManager, which potentially still have the problem. I would like to see that happen, to understand how this happens. So this change intentionally affects older versions too, to possibly reproduce the original problem.

https://bugzilla.redhat.com/show_bug.cgi?id=1778798

(patch is on top of !786 (merged))