libnet: add license info

Signed-off-by: Marko Ratkaj <marko.ratkaj@sartura.hr>

libs/libnet-1.2.x/Makefile

@@ -15,6 +15,7 @@ PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.gz
 PKG_SOURCE_URL:=http://sourceforge.net/projects/libnet-dev/files/
 PKG_MD5SUM:=f051e6e5bdecddb90f77c701c2ca1804
 PKG_MAINTAINER:=Mislav Novakovic <mislav.novakovic@sartura.hr>
+PKG_LICENSE:=GPL-2.0
 
 PKG_FIXUP:=autoreconf
 PKG_INSTALL:=1