RDMA/rtrs-srv: Fix several issues in rtrs_srv_destroy_path_files

RDMA/rtrs-srv: Fix several issues in rtrs_srv_destroy_path_files

There are several issues in the function which is supposed to be paired
with rtrs_srv_create_path_files.

1. rtrs_srv_stats_attr_group is not removed though it is created in
   rtrs_srv_create_stats_files.

2. it makes more sense to check kobj_stats.state_in_sysfs before destroy
   kobj_stats instead of rely on kobj.state_in_sysfs.

3. kobject_init_and_add is used for both kobjs (srv_path->kobj and
   srv_path->stats->kobj_stats), however we missed to call kobject_del
   for srv_path->kobj which was called in free_path.

4. rtrs_srv_destroy_once_sysfs_root_folders is independent of either
   kobj or kobj_stats.

Acked-by: Md Haris Iqbal <haris.iqbal@ionos.com>
Signed-off-by: Guoqing Jiang <guoqing.jiang@linux.dev>
Link: https://lore.kernel.org/r/20221117101945.6317-8-guoqing.jiang@linux.dev
Signed-off-by: Leon Romanovsky <leon@kernel.org>