Bluetooth: Add support for utilizing Fast Advertising Interval

Changes made to add support for fast advertising interval
as per core 4.1 specification, section 9.3.11.2.

A peripheral device entering any of the following GAP modes and
sending either non-connectable advertising events or scannable
undirected advertising events should use adv_fast_interval2
(100ms - 150ms) for adv_fast_period(30s).

         - Non-Discoverable Mode
         - Non-Connectable Mode
         - Limited Discoverable Mode
         - General Discoverable Mode

Signed-off-by: Spoorthi Ravishankar Koppad <spoorthix.k@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>