ipv6: Fix dump of specific table with strict checking

Dump of a specific table with strict checking enabled is looping. The
problem is that the end of the table dump is not marked in the cb. When
dumping a specific table, cb args 0 and 1 are not used (they are the hash
index and entry with an hash table index when dumping all tables). Re-use
args[0] to hold a 'done' flag for the specific table dump.

Fixes: 13e38901 ("net/ipv6: Plumb support for filtering route dumps")
Reported-by: NJakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: NDavid Ahern <dsahern@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/ip6_fib.c

@@ -627,7 +627,11 @@ static int inet6_dump_fib(struct sk_buff *skb, struct netlink_callback *cb)
 			return -ENOENT;
 		}
 
-		res = fib6_dump_table(tb, skb, cb);
+		if (!cb->args[0]) {
+			res = fib6_dump_table(tb, skb, cb);
+			if (!res)
+				cb->args[0] = 1;
+		}
 		goto out;
 	}