systemd-networkd should run with a persistent config in place

Because it doesn't inherit the default set of dependencies, there was
nothing ensuring that it only starts after our /etc got back in place.

Change-Id: I8816ece1b730335bfee392083d1eb6f831376b16
Fixes: https://tree.taiga.io/project/jktjkt-czechlight/task/233
diff --git a/package/czechlight-cfg-fs/etc-overlay.service b/package/czechlight-cfg-fs/etc-overlay.service
index 625e72b..3af78fa 100644
--- a/package/czechlight-cfg-fs/etc-overlay.service
+++ b/package/czechlight-cfg-fs/etc-overlay.service
@@ -2,7 +2,7 @@
 Description=Overlay filesystem over /etc
 DefaultDependencies=no
 Conflicts=umount.target
-Before=local-fs.target umount.target
+Before=local-fs.target umount.target systemd-networkd.service
 After=swap.target \x2eov.mount
 
 [Service]