rhashtable: reset iter when rhashtable_walk_start sees new table

The documentation claims that when rhashtable_walk_start_check()
detects a resize event, it will rewind back to the beginning
of the table.  This is not true.  We need to set ->slot and
->skip to be zero for it to be true.
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

lib/rhashtable.c

@@ -737,6 +737,8 @@ int rhashtable_walk_start_check(struct rhashtable_iter *iter)
 
 	if (!iter->walker.tbl && !iter->end_of_table) {
 		iter->walker.tbl = rht_dereference_rcu(ht->tbl, ht);
+		iter->slot = 0;
+		iter->skip = 0;
 		return -EAGAIN;
 	}