ceph: allow closing session in restarting/reconnect state

CEPH_MDS_SESSION_{RESTARTING,RECONNECTING} are for for mds failover,
they are sub-states of CEPH_MDS_SESSION_OPEN. So __close_session()
should send close request for session in these two state.

Signed-off-by: "Yan, Zheng" <zyan@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>