libxtables: decouple non-xtables parts from header

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
diff --git a/.gitignore b/.gitignore
index 116de2c..97c3004 100644
--- a/.gitignore
+++ b/.gitignore
@@ -18,7 +18,7 @@
 /extensions/targets?.man
 
 /include/xtables.h
-/include/xtables/internal.h
+/include/iptables/internal.h
 
 /aclocal.m4
 /autom4te*.cache