kmod-blacklist: add license

pkgs/os-specific/linux/kmod-blacklist-ubuntu/default.nix

···
     homepage = "https://packages.ubuntu.com/source/zesty/kmod";
     description = "Linux kernel module blacklists from Ubuntu";
     platforms = platforms.linux;
+    license = with licenses; [ gpl2Plus lgpl21Plus ];
   };
 }