Bluetooth: Disable page scan if all whitelisted devices are connected

When we're not connectable and all whitelisted (BR/EDR) devices are
connected it doesn't make sense to keep page scan enabled. This patch
adds code to check for any disconnected whitelist devices and if there
are none take the appropriate action in the hci_update_page_scan()
function to disable page scan.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>