ceph: send oldest_client_tid when renewing caps

Update the oldest_client_tid via the session renew caps msg to
make sure that the MDSs won't pile up the completed request list
in a very large size.

[ idryomov: drop inapplicable comment ]

Link: https://tracker.ceph.com/issues/63364


Signed-off-by: Xiubo Li <xiubli@redhat.com>
Reviewed-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>