Bluetooth: Add LE scan type macros

This patch adds macros for active and passive LE scan type values.
The LE_SCAN_PASSIVE was also defined since it will be used in future
by LE connection routine and GAP Observer Role support.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Acked-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>