Bluetooth: controller: Fix TargetA check as initiator

The existing check for the TargetA address in directed advertising
events was incorrect. In fact the specification states:

"An initiator that has been instructed by the Host to use
Resolvable Private Addresses shall not respond to directed connectable
advertising events that contain Public or Static addresses for the
target’s address (TargetA field)."

Hence, reject TargetA values that have not been successfully resolved
when the controller is generating its own RPAs.

Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>