Bluetooth: BR/EDR: Reset pairing context when needed

When pairing procedure ends regardless of the status, reset flags
strictly related to pairing phase and reset security level.
Thanks that next authentication will get known initial pairing 'context'.

Change-Id: Ie3108c6e28e136ea929e564a6820675cc770cb95
Signed-off-by: Arkadiusz Lichwa <arkadiusz.lichwa@tieto.com>