busybox: give priority of 10

Lots of packages provide this. Usually we don't want the busybox version.

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

@@ -106,5 +106,6 @@ stdenv.mkDerivation rec {
     license = licenses.gpl2;
     maintainers = with maintainers; [ ];
     platforms = platforms.linux;
+    priority = 10;
   };
 }