add nics for eths to vms from numbers

modules/vm.nix

@@ -1,6 +1,22 @@
-{ lib, modulesPath, ... }:
+{ lib, modulesPath, numbers, ... }:
 with lib;
 
+let
+  makeNic = host: iface:
+    let { matchMac, iface, media, ... } = numbers.api.hostIface host iface;
+    in
+      if media != "eth" then [] else
+        [
+          "-nic bridge,id=${iface},br=${iface},model=virtio,mac=${matchMac}"
+        ];
+  makeNics = host: concatMap (makeNic host) (numbers.api.hostIfaces host);
+  makeQemuNetworkingOptions = host:
+    (makeNics host) ++ [
+      "-net nic,netdev=user.0,model=virtio"
+      "-netdev user,id=user.0,\${QEMU_NET_OPTS:+,$QEMU_NET_OPTS}"
+    ];
+in
+
 {
   imports = [
     "${modulesPath}/virtualisation/qemu-vm.nix"
@@ -9,5 +25,6 @@ with lib;
 
   config = {
     virtualisation.graphics = false;
+    virtualisation.qemu.networkingOptions = makeQemuNetworkingOptions config.networking.hostName;
   };
 }