Desktop/NetworkManager: don't manage tailscale's interface

roles/desktop/services/networkmanager.nix

@@ -1,7 +1,14 @@
-{ ... }:
+{ config, ... }:
+
+let
+  tailscaleName = config.services.tailscale.interfaceName;
+in
 
 {
   networking.networkmanager = {
     enable = true;
+    unmanaged = [
+      "interface-name:${tailscaleName}"
+    ];
   };
 }