d/control: update build-deps

Put build-deps required by the nftables backend.
Signed-off-by: Arturo Borrero Gonzalez <arturo.borrero.glez@gmail.com>

debian/control

@@ -2,7 +2,7 @@ Source: iptables
 Section: net
 Priority: important
 Maintainer: Laurence J. Lane <ljlane@debian.org>
-Build-Depends: debhelper (>= 9), autoconf, automake, libtool (>=2.2.6), libnfnetlink-dev, libnetfilter-conntrack-dev, libnetfilter-conntrack3, dh-autoreconf
+Build-Depends: debhelper (>= 9), autoconf, automake, libtool (>=2.2.6), libnfnetlink-dev, libnetfilter-conntrack-dev, libnetfilter-conntrack3, dh-autoreconf, libnftnl-dev, libmnl-dev, flex, bison
 Standards-Version: 3.9.5
 Homepage: http://www.netfilter.org/