nftables: clean up Makefile

Add PKG_LICENSE_FILES. Use SPDX.

Signed-off-by: Nick Hainke <[email protected]>

package/network/utils/nftables/Makefile

@@ -1,7 +1,6 @@
-# Copyright (C) 2015 OpenWrt.org
+# SPDX-License-Identifier: GPL-2.0-only
 #
-# This is free software, licensed under the GNU General Public License v2.
-# See /LICENSE for more information.
+# Copyright (C) 2015 OpenWrt.org
 #
 
 include $(TOPDIR)/rules.mk
@@ -13,8 +12,10 @@ PKG_RELEASE:=1
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.bz2
 PKG_SOURCE_URL:=https://netfilter.org/projects/$(PKG_NAME)/files
 PKG_HASH:=47c4eba0105ebd3ffa89553e0702ccb34d8906a91f72ced58ab0d992b29c7748
+
 PKG_MAINTAINER:=
 PKG_LICENSE:=GPL-2.0
+PKG_LICENSE_FILES:=COPYING
 
 PKG_FIXUP:=autoreconf
 PKG_INSTALL:=1