src: remove inclusion of iptables.h

iptables.h and ip6tables.h only include declarations internal to
iptables (specifically iptables.c and ip6tables.c), as most of the
public API has been moved to xtables.h a few months ago.

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
Signed-off-by: Patrick McHardy <kaber@trash.net>
diff --git a/extensions/libip6t_rt.c b/extensions/libip6t_rt.c
index 25e410c..c1f72af 100644
--- a/extensions/libip6t_rt.c
+++ b/extensions/libip6t_rt.c
@@ -5,7 +5,7 @@
 #include <stdlib.h>
 #include <getopt.h>
 #include <errno.h>
-#include <ip6tables.h>
+#include <xtables.h>
 /*#include <linux/in6.h>*/
 #include <linux/netfilter_ipv6/ip6t_rt.h>
 #include <sys/types.h>