ipv6: properly check return value in inet6_dump_all()

Make sure we call fib6_dump_end() if it happens that skb->len
is zero. rtnl_dump_all() can reset cb->args on the next loop
iteration there.

Fixes: 08e814c9 ("net/ipv6: Bail early if user only wants cloned entries")
Fixes: ae677bbb ("net: Don't return invalid table id error when dumping all families")
Signed-off-by: Alexey Kodanev <alexey.kodanev@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/ip6_fib.c

@@ -591,7 +591,7 @@ static int inet6_dump_fib(struct sk_buff *skb, struct netlink_callback *cb)
 
 	/* fib entries are never clones */
 	if (arg.filter.flags & RTM_F_CLONED)
-		return skb->len;
+		goto out;
 
 	w = (void *)cb->args[2];
 	if (!w) {
@@ -621,7 +621,7 @@ static int inet6_dump_fib(struct sk_buff *skb, struct netlink_callback *cb)
 		tb = fib6_get_table(net, arg.filter.table_id);
 		if (!tb) {
 			if (arg.filter.dump_all_families)
-				return skb->len;
+				goto out;
 
 			NL_SET_ERR_MSG_MOD(cb->extack, "FIB table does not exist");
 			return -ENOENT;