RDMA/rtrs-srv: Use sysfs_remove_file_self for disconnect

Remove self first to avoid deadlock, we don't want to
use close_work to remove sess sysfs.

Fixes: 91b11610 ("RDMA/rtrs: server: sysfs interface functions")
Link: https://lore.kernel.org/r/20201217141915.56989-5-jinpu.wang@cloud.ionos.com


Signed-off-by: Jack Wang <jinpu.wang@cloud.ionos.com>
Tested-by: Lutz Pogrell <lutz.pogrell@cloud.ionos.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>