This permits using method_set_hostname but still denies
method_set_static_hostname. As a result DHCP clients can now always set
the transient hostname via the SetHostname method of the D-Bus interface
of systemd-hostnamed (org.freedesktop.hostname1.set-hostname).
If the NixOS option networking.hostName is set to an empty string (or
"localhost") the static hostname (kernel.hostname but NOT /etc/hostname)
will additionally be updated (this is intended).
From "man hostnamectl": The transient hostname is a fallback value
received from network configuration. If a static hostname is set, and is
valid (something other than localhost), then the transient hostname is
not used.
Fix#74847.
Note: It's possible to restrict access to the org.freedesktop.hostname1
interface using Polkit rules.
483dbe9237