Bluetooth: Add support for reading LE White List Size

The LE White List Size is necessary to be known before attempting to
feed the controller with any addresses intended for the white list. This
patch adds the necessary HCI command sending to the HCI init sequence.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>