xtables: fix typo in add_entry for the IPv6 case

It should pass zero, instead of the 'append' boolean.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/iptables/xtables.c b/iptables/xtables.c
index 7a6509a..3035546 100644
--- a/iptables/xtables.c
+++ b/iptables/xtables.c
@@ -442,7 +442,7 @@
 				       &d.mask.v6[j], sizeof(struct in6_addr));
 				if (append) {
 					ret = nft_rule_append(h, chain, table,
-							      cs, append,
+							      cs, 0,
 							      verbose);
 				} else {
 					ret = nft_rule_insert(h, chain, table,