feat(router0-dmz0,sj-srv1): use bridged macvlan as main dmz interface

this allows guest VMs to communicate with the host via their macvtap
connection.

nix/os/devices/sj-srv1/system.nix

@@ -25,12 +25,12 @@
   networking.usePredictableInterfaceNames = false;
 
   networking.useNetworkd = true;
-  networking.useDHCP = true;
+  networking.useDHCP = false;
 
   networking.nat = {
     enable = true;
-    externalInterface = "eth0";
     internalInterfaces = ["br0"];
+    externalInterface = "dmz0";
   };
 
   networking.bridges = {
@@ -49,8 +49,40 @@
     };
   };
 
+  systemd.network.netdevs."10-dmz0" = {
+    enable = true;
+    netdevConfig = {
+      Name = "dmz0";
+      Kind = "macvlan";
+      MACAddress = "1c:69:7a:07:08:6f";
+    };
+
+    macvlanConfig = {
+      Mode = "bridge";
+    };
+  };
+
+  systemd.network.networks."20-eth0" = {
+    enable = true;
+    matchConfig.Name = "eth0";
+
+    # TODO: i'm not sure if and if so why this is required
+    macvlan = [
+      "dmz0"
+    ];
+
+    DHCP = "no";
+  };
+
+  systemd.network.networks."30-dmz0" = {
+    enable = true;
+    matchConfig.Name = "dmz0";
+    DHCP = "yes";
+  };
+
   boot.kernel.sysctl = {
     "net.ipv4.ip_forward" = 1;
+    "net.ipv6.ip_forward" = 1;
   };
 
   # virtualization