[GATT Client] Delivery ATT error code to higher layer

[GATT Client] Delivery ATT error code to higher layer

[Problem] ATT error code is not passed to application.

[Cause & Measure] GATT application need to know ATT
error code to handling error case. Specially application
error code defined by a higher layer specification.

[Checking Method] GATT error handling

Change-Id: I37747073962baa2b1098eb801ce033fb0b0c4c85
Signed-off-by: Gowtham Anandha Babu <gowtham.ab@samsung.com>