Revert this change. One problem is that none of the current GUIs
(nm-connection-editor, gnome-control-center, plasma-nm) expose the
dns-priority option. So, users tend to have their profile value set to
0. Changing the default means for them not only a change in behavior,
but its hard to fix via the GUI.

Also, what other call DNS leaks, is Split DNS to some. Both uses make
sense, but have conflicting goals. The default cannot accommodate both
at the same time.

Also, with split DNS enabled (dnsmasq, systemd-resolved), the concern
for DNS leaks is smaller. Imagine:

  Wi-Fi profile with ipv4.dns-priority (effectively) 100, domain "example.com".
  VPN profile with ipv4.dns-priority (effectively) 50 and a default route.

That is a common setup that one gets by default (and what probably many
users have today). In such a case with split DNS enabled, the Wi-Fi's DNS
server only sees requests for "*.example.com". So, it does not leak
everything.

Hence, revert this change before 1.28.0 release to the earlier behavior.

This reverts commit af13081b.

!688
(cherry picked from commit ff71bbdc)