gatt: Add support for storing Service Changed CCC value

gatt: Add support for storing Service Changed CCC value

This adds support for storing CCC value of Service Changed
characteristic. Once bluetoothd is restart stored values are read
and any device subscribed to indications will receive Service Changed
indication with 0x00010-0xffff value. This is to invalidate any
non-core services since there is no way to verify if applications
will register their services in same order (or at all).

This fix accessing invalid handles by stacks that rely only on Service
Changed indication for rediscovery ie. Apple iOS.

Change-Id: I742bb2520a02d73aa69ca0ab5ac8c885e701c498
Signed-off-by: Amit Purwar <amit.purwar@samsung.com>