netfilter: nft_nat: don't dump port information if unset

Don't include port information attributes if they are unset.
Reported-by: Ana Rey <anarey@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nft_nat.c

@@ -175,12 +175,14 @@ static int nft_nat_dump(struct sk_buff *skb, const struct nft_expr *expr)
 	if (nla_put_be32(skb,
 			 NFTA_NAT_REG_ADDR_MAX, htonl(priv->sreg_addr_max)))
 		goto nla_put_failure;
-	if (nla_put_be32(skb,
-			 NFTA_NAT_REG_PROTO_MIN, htonl(priv->sreg_proto_min)))
+	if (priv->sreg_proto_min) {
+		if (nla_put_be32(skb, NFTA_NAT_REG_PROTO_MIN,
+				 htonl(priv->sreg_proto_min)))
 			goto nla_put_failure;
-	if (nla_put_be32(skb,
-			 NFTA_NAT_REG_PROTO_MAX, htonl(priv->sreg_proto_max)))
+		if (nla_put_be32(skb, NFTA_NAT_REG_PROTO_MAX,
+				 htonl(priv->sreg_proto_max)))
 			goto nla_put_failure;
+	}
 	return 0;
 
 nla_put_failure: