netfilter: ipset: fix ip_set_flush return code

ip_set_flush returned -EPROTO instead of -IPSET_ERR_PROTOCOL, fixed

Signed-off-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/net/netfilter/ipset/ip_set_core.c b/net/netfilter/ipset/ip_set_core.c
index 72d1ac6..8041bef 100644
--- a/net/netfilter/ipset/ip_set_core.c
+++ b/net/netfilter/ipset/ip_set_core.c
@@ -815,7 +815,7 @@
 	ip_set_id_t i;
 
 	if (unlikely(protocol_failed(attr)))
-		return -EPROTO;
+		return -IPSET_ERR_PROTOCOL;
 
 	if (!attr[IPSET_ATTR_SETNAME]) {
 		for (i = 0; i < ip_set_max; i++)