nftables: fix substituted file location

[Shawn8901]

Description of changes

When splitting out the python part of nftables it broke the substituteInPlace, as there is a setSourceRoot set.
So when patching, its already in the py folder.

That should unbreak pythonPackages.nftables and its dependants.

https://hydra.nixos.org/build/258436548

I just tried to build it and firewalld as dependency.

ZHF: #309482

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 24.05 Release Notes (or backporting 23.05 and 23.11 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

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[Shawn8901]

Result of nixpkgs-review pr 309648 run on x86_64-linux 1

6 packages built:

• firewalld
• firewalld-gui
• python311Packages.nftables
• python311Packages.nftables.dist
• python312Packages.nftables
• python312Packages.nftables.dist