linuxPackages.dpdk-kmods: move env variables into env for structuredAttrs

pkgs/os-specific/linux/dpdk-kmods/default.nix

@@ -20,14 +20,15 @@ stdenv.mkDerivation rec {
   makeFlags = kernelModuleMakeFlags ++ [
     "INSTALL_MOD_PATH=${placeholder "out"}"
   ];
-  KSRC = "${kernel.dev}/lib/modules/${kernel.modDirVersion}/build";
+
+  env.KSRC = "${kernel.dev}/lib/modules/${kernel.modDirVersion}/build";
 
   nativeBuildInputs = kernel.moduleBuildDependencies;
 
   preBuild = "cd linux/igb_uio";
 
   installPhase = ''
-    make -C ${KSRC} M=$(pwd) modules_install $makeFlags
+    make -C ${env.KSRC} M=$(pwd) modules_install $makeFlags
   '';
 
   enableParallelBuilding = true;