gatt-server : Check the validation of app before sending notification

gatt-server : Check the validation of app before sending notification

[Model] All
[BinType] AP
[Customer] OPEN

[Issue#] N/A
[Request] Internal
[Occurrence Version] N/A

[Problem] bluez got crash
[Cause & Measure] If gatt server app is terminated abnormally
 while sending notification, bluetoothd access to invalid proxy of chrc.
 So we need to check the object path of notification characteristic
 path : /com/4260/service1/characteristic2
[Checking Method] GATT notification

[Team] Basic Connection
[Developer] Injun Yang
[Solution company] Samsung
[Change Type] Specification change

Change-Id: I85f0643d8e033935308ed5ae1ef93274f95385d7