Bluetooth: BR/EDR: Refactor internals of 'Cancel' authentication API

For better code readability use 'switch-case' statement selecting valid
authentication cancel method. Adds also legacy pairing (pre-SSP) as first
item in valid paring method set.

Change-Id: I4d9c5178526cd5210b844878360d12b58b99a24f
Signed-off-by: Arkadiusz Lichwa <arkadiusz.lichwa@tieto.com>