ceph: never send metrics if disable_send_metrics is set

Even the 'disable_send_metrics' is true so when the session is
being opened it will always trigger to send the metric for the
first time.

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