When reconnecting the session but if it is denied by the MDS due
to client was in blacklist or something else, kclient will receive
a session close reply, and we will never see the important log:

"ceph:  mds%d reconnect denied"

And with the confusing log:

"ceph:  handle_session mds0 close 0000000085804730 state ??? seq 0"

Let's keep the session state until its memories is released.
Signed-off-by: Xiubo Li <xiubli@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>