linuxPackages.wireguard: fix build

Ensure that only module-related targets from the project's Makefile are
built.

Co-authored-by: elseym <[e-mail]>
Co-authored-by: Franz Pletz <[e-mail]>
(cherry picked from commit 2c3ab523d3fc47c2bbb1a34e09096e02be884fde)

pkgs/os-specific/linux/wireguard/default.nix

···
 
   nativeBuildInputs = [ perl ] ++ kernel.moduleBuildDependencies;
 
-  buildPhase = "make module";
+  buildFlags = [ "module" ];
+  installTargets = [ "module-install" ];
 
   meta = with stdenv.lib; {
     inherit (wireguard-tools.meta) homepage license maintainers;