Keep local IRK in permanent storage

Keep local IRK in permanent storage

[Model] COMMON
[BinType] AP
[Customer] OPEN

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

[Problem] When local IRK is changed, iOS rejects re-pairing request (iOS issue).
 This issue happens in below scenario.
 1. Pair with iOS
 2. Factory-reset DUT
 3. Try to pair with iOS again without unpairing on iOS
 4. iOS sends SMP pairing error with "Unspecified reason". So until user
   unpairs DUT on iOS, re-pairing is not possible.

 And when local IRK is not distributed at BLE pairing with some android
 devices, those devices cannot connect to DUT again via BLE (Android issue).
 1. Pair with Galaxy A5 2016 / Note 4 via BLE
 2. Disconnect
 3. Try to connect again via BLE
 4. A5 2016 / Note 4 try to connect to DUT using 00:00:00:00:00:00
   address. So it is failed.

 To solve these issues, DUT distributes a IRK. And after resetting DUT,
 retain the IRK.
[Cause & Measure] Compatibility issues with other OS's.
[Checking Method]
 ===
 1. Pair with iOS
 2. Factory-reset DUT
 3. Try to pair with iOS again without unpairing on iOS
 4. iOS sends SMP pairing error with "Unspecified reason". So until user
   unpairs DUT on iOS, re-pairing is not possible.
 ===
 1. Pair with Galaxy A5 2016 / Note 4 via BLE
 2. Disconnect
 3. Try to connect again via BLE
 4. A5 2016 / Note 4 try to connect to DUT using 00:00:00:00:00:00
 ===

[Team] Basic connection
[Developer] Seungyoun Ju
[Solution company] Samsung
[Change Type] Specification change

Change-Id: Ib8d2d2746d27583aa1ed36be785f0df44a95918e
Signed-off-by: DoHyun Pyun <dh79.pyun@samsung.com>