ceph: add session already open notify support

If the connection was accidently closed due to the socket issue or
something else the clients will try to open the opened sessions, the
MDSes will send the session open reply one more time if the clients
support the notify feature.

When the clients retry to open the sessions the s_seq will be 0 as
default, we need to update it anyway.

Link: https://tracker.ceph.com/issues/53911


Signed-off-by: Xiubo Li <xiubli@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>