rgw: version bucket stats not correct
steps to reproduce:
1、create a bucket, enable versioning
2、put a obj named obja
3、suspended the bucket versioning
4、put obja again
5、simple delete obja
6、bucket_stats show than there are still 2 objs in the bucket. Acutuall, the null version was replaced by null delete_marker. There is only 1 objs in the bucket.
in the function rgw_bucket_link_olh. When link a null version delete_marker, should not do other_obj.unlink().
other_obj.unlink will remove the idx. So when deleting the previous null version idx can't be find and will not do unaccount_entry. The bucket stats is not updated.