gatt: Add org.bluez.Error.InvalidOffset for long read procedure

gatt: Add org.bluez.Error.InvalidOffset for long read procedure

This patch adds handling of invalid offset error for gatt database in
case if offset in read blob would be invalid.

"The Read Blob Request is repeated until the Read Blob Response’s Part
Attribute Value parameter is zero or an Error Response is sent by the server
with the Error Code set to Invalid Offset." Bluetooth Core 5.0, 4.12.2

"If the prepare Value Offset is greater than the current length of the attribute
value then all pending prepare write values shall be discarded for this client,
the queue shall be cleared and then an Error Response shall be sent with the
«Invalid Offset»." Bluetooth Core 5.0, 3.4.6.3

Change-Id: I678ca6984bde4502a3b325fd1822d21d98e6a1a9
Signed-off-by: Amit Purwar <amit.purwar@samsung.com>