src: move all iptables pieces into a separate directory

(Unclutter top-level dir)

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
diff --git a/configure.ac b/configure.ac
index f3de3d3..4fba167 100644
--- a/configure.ac
+++ b/configure.ac
@@ -111,6 +111,7 @@
 AC_SUBST([libxtables_vmajor])
 
 AC_CONFIG_FILES([Makefile extensions/GNUmakefile include/Makefile
+	iptables/Makefile iptables/xtables.pc
 	libipq/Makefile libiptc/Makefile libiptc/libiptc.pc utils/Makefile
-	include/xtables.h include/iptables/internal.h xtables.pc])
+	include/xtables.h include/iptables/internal.h])
 AC_OUTPUT