systemd: add hostname fallback when polkit is not available
When polkit is not available, networkd will not have permissions
to call hostnamed's dbus methods, as it runs without privileges.
To solve this, when building without polkit, make a new PACKAGECONFIG
'polkit_hostnamed_fallback' available which changes hostnamed so that
it runs as the 'systemd-network' user, the same as networkd, so that
the authorization works (and also with CAP_SYS_ADMIN since it loses
root).
Also run it with a separate 'systemd-hostname' group which also owns
the bus, to avoid giving the 'systemd-network' additional privileges.
Signed-off-by: Luca Boccassi <luca.boccassi@microsoft.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
