netcardconfig doesn't properly handle this section and it disappears
when configuring network devices then.
Rewriting netcardconfig is on our agenda (see
https://github.com/grml/grml-network/issues/11), until we get there
let's make sure the status quo works as good as possible.
Take over wording based on what ifupdown's postinst script uses.
# ${GRML_FAI_CONFIG}/config/scripts/GRMLBASE/35-network script, using
# ${GRML_FAI_CONFIG}/config/files/etc/network/interfaces/GRMLBASE
+# interfaces(5) file used by ifup(8) and ifdown(8)
+
+# Include files from /etc/network/interfaces.d:
+source /etc/network/interfaces.d/*
+
# The loopback interface
auto lo
iface lo inet loopback
-source /etc/network/interfaces.d/*