Bluetooth: Clear pairing flag if all keys have been distributed

This fixes the bug that affected pairing as peripheral.
With this patch pairing flag is cleared and timeout timer stops
if all keys has been distributed.

Change-Id: If7575197d5a42a0ca5bb158ea5607934e92abb81
Signed-off-by: Mariusz Skamra <mariusz.skamra@tieto.com>