netfilter: ipset: Fix rename concurrency with listing

Shijie Luo reported that when stress-testing ipset with multiple concurrent
create, rename, flush, list, destroy commands, it can result

ipset <version>: Broken LIST kernel message: missing DATA part!

error messages and broken list results. The problem was the rename operation
was not properly handled with respect of listing. The patch fixes the issue.

Reported-by: Shijie Luo <luoshijie1@huawei.com>
Signed-off-by: Jozsef Kadlecsik <kadlec@netfilter.org>