networkmanager-l2tp: 1.20.4 -> 1.20.10 (#229312)

Fixes build after ppp update.
https://hydra.nixos.org/build/217889566/nixlog/4/tail
https://github.com/nm-l2tp/NetworkManager-l2tp/releases

pkgs/tools/networking/networkmanager/l2tp/default.nix

···
 stdenv.mkDerivation rec {
   name = "${pname}${lib.optionalString withGnome "-gnome"}-${version}";
   pname = "NetworkManager-l2tp";
-  version = "1.20.4";
+  version = "1.20.10";
 
   src = fetchFromGitHub {
     owner = "nm-l2tp";
     repo = "network-manager-l2tp";
     rev = version;
-    sha256 = "VoqPjMQILBYemRE5VD/XwhWi9zL9QxxHZJ2JKtGglFo=";
+    hash = "sha256-EfWvh4uSzWFadZAHTqsKa3un2FQ6WUbHLoHo9gSS7bE=";
   };
 
   patches = [