src: remove dependency on libiptc headers

xtables.h does not need really need libxtc.h, and we can drop it from
the install as it is internal-only.

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
Signed-off-by: Patrick McHardy <kaber@trash.net>
diff --git a/include/iptables.h b/include/iptables.h
index ecc7168..99e8e1e 100644
--- a/include/iptables.h
+++ b/include/iptables.h
@@ -1,8 +1,9 @@
 #ifndef _IPTABLES_USER_H
 #define _IPTABLES_USER_H
 
-#include "xtables.h"
-#include "libiptc/libiptc.h"
+#include <netinet/ip.h>
+#include <xtables.h>
+#include <libiptc/libiptc.h>
 
 #ifndef IPT_SO_GET_REVISION_MATCH /* Old kernel source. */
 #define IPT_SO_GET_REVISION_MATCH	(IPT_BASE_CTL + 2)