nixosTests.systemd-initrd.bridge: fix failing test

Since slave interfaces of a bridge cannot be assigned IP addresses, we
must prevent IPs from being assigned to them via the test framework
modules. Since c6f6c28218, all nodes get
ipv6 addresses by default, so we must ensure IP addresses of any type
don't get assigned to the bridge slave interfaces.

nixos/tests/systemd-initrd-bridge.nix

@@ -24,20 +24,23 @@
           serviceConfig.Type = "oneshot";
         };
 
-        networking.primaryIPAddress = "192.168.1.${toString config.virtualisation.test.nodeNumber}";
+        networking.primaryIPAddress = lib.mkForce "192.168.1.${toString config.virtualisation.test.nodeNumber}";
+
+        virtualisation.interfaces.eth1 = {
+          vlan = 1;
+          assignIP = false;
+        };
+        virtualisation.interfaces.eth2 = {
+          vlan = 2;
+          assignIP = false;
+        };
 
-        virtualisation.vlans = [
-          1
-          2
-        ];
         networking.bridges.br0.interfaces = [
           "eth1"
           "eth2"
         ];
 
         networking.interfaces = {
-          eth1.ipv4.addresses = lib.mkForce [ ];
-          eth2.ipv4.addresses = lib.mkForce [ ];
           br0.ipv4.addresses = [
             {
               address = config.networking.primaryIPAddress;