nvidia-x11: strip debug info from the kernel modules at install

The modules record absolute `${kernel.dev}` paths in DWARF that the fixup
`strip` can't reach as it's already compressed, so `allowedReferences = [ ]`
only passes when compression hides the hash. When setting `MODULE_COMPRESS_ZSTD`,
the hash is not hidden, causing this module to fail to build.

This commit strips the module before compression.

pkgs/os-specific/linux/nvidia-x11/kernel-modules.nix

@@ -47,6 +47,7 @@ stdenv.mkDerivation {
     ];
 
   buildTargets = [ "modules" ];
+  installFlags = [ "INSTALL_MOD_STRIP=1" ];
   installTargets = [ "modules_install" ];
   enableParallelBuilding = true;