Bluetooth: Kconfig: Introduce new BT_SCAN_WITH_IDENTITY option

Even with the privacy feature disabled, the stack has so far defaulted
to using an NRPA for active scanning, in order to protect privacy.
This is mainly because it is not always clear that scanning for other
devices may risk revealing the local identity.

There may however be use cases where such revealing is actively
desired, so introduce a new option for this (which defaults to
disabled).

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>