bgpwtf/edge01: as-deployed: add qemu-bridge-helper config to fix anchorvm

Change-Id: I305c498f8332de8addac435da57ba88e1b34c7f0

bgpwtf/machines/modules/anchorvm.nix

@@ -24,6 +24,15 @@ in {
     };
   };
 
+  config.environment = {
+    # qemu-bridge-helper (needed for -nic bridge) requires this file to exist.
+    # We're running as root and don't care about the ACL functionality, so just
+    # make a minimal file that allows the interface.
+    # This snippet stolen from nixpkgs//libvirtd.nix
+    etc."qemu/bridge.conf".text = lib.concatMapStringsSep "\n" (e:
+      "allow ${e}") [cfg.bridge];
+  };
+
   config.systemd.services.anchorvm = {
     wantedBy = [ "multi-user.target" ];
     after = [