Many distributions ship systemd-networkd as a separate file so we
need to be able to ship the tmpfiles networkd entries as part of
that separate networkd package. Let's split the networkd entries
into a separate file to make that possible.
HAVE_SMACK_RUN_LABEL was dropped back in 348b44372f,
so one line in etc.conf was not rendered as expected ;(
Checking if names are defined is paying for itself!