proxmox: fix network interface renaming

Use systemd .link files which are "relatively futureproof" according
to https://wiki.debian.org/NetworkInterfaceNames .

roles/proxmox/tasks/network.yml

@@ -1,8 +1,11 @@
 - name: Add rules to rename network interfaces
   template:
-    dest: /etc/udev/rules.d/10-network.rules
+    dest: "/etc/systemd/network/10-{{ item.name }}.link"
-    src: 10-network.rules.j2
+    src: interface.link.j2
-    mode: 0644
+    mode: "0644"
+  loop: "{{ interfaces | selectattr('mac_address') }}"
+  loop_control:
+    label: "{{ item.name }}"
   notify: reboot
 
 - name: Set up bridges

templates/interface.link.j2

@@ -0,0 +1,5 @@
+[Match]
+MACAddress={{ item.mac_address | lower }}
+
+[Link]
+Name={{ item.name }}