Make IP address assignment work with libvirt

The systemd-networkd script in vmdebootstrap that is used to build the
Debian libvirt vagrant boxes is a bit too eager assigning DHCP to
network interfaces. This patch changes the network script to only take
care of the primary network interface (first non loopback).

Vagrantfile

@@ -5,7 +5,7 @@ Vagrant.configure(2) do |config|
   config.vm.box = "debian/buster64"
 
   config.vm.hostname = "gvaldap.local"
-  config.vm.network "private_network", ip: "172.16.3.3", lxc__bridge_name: 'vlxcbr1'
+  config.vm.network :private_network, :ip => "172.16.3.3"
 
   config.vm.network "forwarded_port", guest: 8000, host: 8001
 
@@ -16,6 +16,8 @@ Vagrant.configure(2) do |config|
       libvirt.memory = 1024
   end
 
+  config.vm.provision :shell, path: "change-vmdebootstrap-default-dhcp.sh"
+
   config.vm.provision :salt do |salt|
       salt.bootstrap_options = "-x python3"
       salt.minion_id = "gvaldap"

change-vmdebootstrap-default-dhcp.sh

@@ -0,0 +1,15 @@
+#!/bin/sh
+
+set -e
+
+debootstrap_network=/etc/systemd/network/99-dhcp.network
+
+if grep -q '^Name=\\*' "${debootstrap_network}"; then
+  primary_nic=$(ls -1 /sys/class/net | grep -v lo |sort | head -1)
+  sed -i "s/^Name=e\\*/Name=${primary_nic})/" \
+    "${debootstrap_network}"
+  systemctl restart systemd-networkd.service
+  echo "Changed systemd network configuration"
+else
+  echo "Systemd network configuration has already been changed"
+fi