nixos/networkmanager: fix merging options

Incorrect merging of modules resulted in dhcpcd being enabled causing flaky network connection.

NixOS#64364

Fixing it uncovered an infinite recursion from the same commit, previously masked by the incorrect merge.

We can just drop the `mkDefault` for `networking.wireless.enable` as it is already `false` by default.

Closes: NixOS#72416

nixos/modules/services/networking/networkmanager.nix

@@ -456,15 +456,19 @@ in {
     };
 
     # Turn off NixOS' network management when networking is managed entirely by NetworkManager
-    networking = (mkIf (!delegateWireless) {
-      useDHCP = false;
-      # Use mkDefault to trigger the assertion about the conflict above
-      wireless.enable = mkDefault false;
-    }) // (mkIf cfg.enableStrongSwan {
-      networkmanager.packages = [ pkgs.networkmanager_strongswan ];
-    }) // (mkIf enableIwd {
-      wireless.iwd.enable = true;
-    });
+    networking = mkMerge [
+      (mkIf (!delegateWireless) {
+        useDHCP = false;
+      })
+
+      (mkIf cfg.enableStrongSwan {
+        networkmanager.packages = [ pkgs.networkmanager_strongswan ];
+      })
+
+      (mkIf enableIwd {
+        wireless.iwd.enable = true;
+      })
+    ];
 
     security.polkit.extraConfig = polkitConf;