Bluetooth: controller: Correct adv, scan and init state checks

For whitelist and resolving list handling, avoid trying to start the
advertiser and scanner roles when they are already running.
Additionally, and since simultaneous scanning and initiating is not
supported, correctly report this to the host both in the supported
states and in the HCI command via an error code, instead of silently
disabling scanning.

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