iptables: update .gitignore

Ignore xtables-config-* generated by flex and bison.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/iptables/.gitignore b/iptables/.gitignore
index 31baf7d..6c0ade1 100644
--- a/iptables/.gitignore
+++ b/iptables/.gitignore
@@ -11,5 +11,8 @@
 /iptables-static
 /iptables-xml
 /xtables-multi
+/xtables-config-parser.c
+/xtables-config-parser.h
+/xtables-config-syntax.c
 
 /xtables.pc