Modify logic for subscribe callback and bug fixed.

Modify logic for subscribe callback and bug fixed.

this patch included,
1. modify logic for subscribe callback.
   call the user subscriberquestcallback function always.
2. bug fixed for NSProviderUnsetConsumerTopic.

Change-Id: Iad177bdf56cc7932ba1b95c157496d47ab6f9132
Signed-off-by: jaesick.shin <jaesick.shin@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/11923
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Uze Choi <uzchoi@samsung.com>
(cherry picked from commit e6cfc565ae20673e2cc71ca4c4ee05473b49ee77)
Reviewed-on: https://gerrit.iotivity.org/gerrit/12439