nftables: set _GNU_SOURCE where needed.

srcpkgs/nftables/template

@@ -1,7 +1,7 @@
 # Template file for 'nftables'
 pkgname=nftables
 version=0.4
-revision=2
+revision=3
 build_style=gnu-configure
 configure_args="--sbindir=/usr/bin CONFIG_MAN=y DB2MAN=docbook2man"
 hostmakedepends="pkg-config docbook2x flex bison"
@@ -13,6 +13,9 @@ homepage="http://netfilter.org/projects/nftables/"
 distfiles="http://www.netfilter.org/projects/${pkgname}/files/${pkgname}-${version}.tar.bz2"
 checksum=f6ca69b75c68915f9f3a3972274ec68354dfbbcfc0b9fc55c813a0525c351d3c
 
+post_extract() {
+	sed -i '1i#include "config.h"' src/proto.c
+}
 post_install() {
 	vsv $pkgname
 }