networkd: also add IPv6 DNS servers by default
networkd: network - store DNS servers in List rather than Set

This way we preserve the order of preference.
networkd: manager - read fallback DNS servers from config file

We will still use the compiled-in defaults if no DNS entry exists in the config file.
logind: allow suspending if there are no displays

With proprietary graphics drivers, there won't be any 'drm' devices in
sysfs, so logind will never suspend the system upon closing the lid,
even if only one (internal) display is connected. This has been reported
by multiple users so far.

IMHO, it's better to suspend the system in this case for safety reasons,
to avoid having nvidia blob users' laptops overheat, for the same reason
that sleep inhibitors are overridden (LidSwitchIgnoreInhibited=yes).
core: let selinux_setup() load policy more than once

When you switch-root into a new root that has SELinux policy, you're
supposed to to run selinux_init_load_policy() to set up SELinux and load
policy. Normally this gets handled by selinux_setup().

But if SELinux was already initialized, selinux_setup() skips loading
policy and returns 0. So if you load policy normally, and then you
switch-root to a new root that has new policy, selinux_setup() never
loads the new policy. What gives?

As far as I can tell, this check is an artifact of how selinux_setup()
worked when it was first written (see commit c4dcdb9 / systemd v12):

  * when systemd starts, run selinux_setup()
  * if selinux_setup() loads policy OK, restart systemd

So the "if policy already loaded, skip load and return 0" check was
there to prevent an infinite re-exec loop.

Modern systemd only calls selinux_setup() on initial load and after
switch-root, and selinux_setup() no longer restarts systemd, so we don't
need that check to guard against the infinite loop anymore.

So: this patch removes the "return 0", thus allowing selinux_setup() to
actually perform SELinux setup after switch-root.

We still want to check to see if SELinux is initialized, because if
selinux_init_load_policy() fails *but* SELinux is initialized that means
we still have (old) policy active. So we don't need to halt if
enforce=1.
networkd: add missing files