Update logic of callback when provider discovered.

Update logic of callback when provider discovered.

When consumer discover already discovered provider as unsubscribing,
does not callback to upper layer before,
but we decide to callback to upper layer, so related logic is updated.

Change-Id: Iddeb4577f94f941473452ad035949aaf7c135914
Signed-off-by: KIM JungYong <jyong2.kim@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/11499
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Uze Choi <uzchoi@samsung.com>