linuxPackages.rtl8814au: parallel build

So much faster.  Tested at -j48.

pkgs/os-specific/linux/rtl8814au/default.nix

@@ -29,6 +29,8 @@ stdenv.mkDerivation {
     mkdir -p "$out/lib/modules/${kernel.modDirVersion}/kernel/net/wireless/"
   '';
 
+  enableParallelBuilding = true;
+
   meta = with lib; {
     description = "Realtek 8814AU USB WiFi driver";
     homepage = "https://github.com/morrownr/8814au";