Add the interface to start / stop visibility timer

Add the interface to start / stop visibility timer

[Problem] Visibility timer is not stopped when connectable mode is
 turned off.
[Cause & Measure] This patch adds the interface to control visibility
 timer in event handler module.
[Checking Method] Turn on limited discoverable mode -> Turn off
 connectable mode -> Check discoverable timeout event

Change-Id: I528b4093427bbda9e9fac4e4ce1b72b1ffb41873
Signed-off-by: Seungyoun Ju <sy39.ju@samsung.com>
Signed-off-by: DoHyun Pyun <dh79.pyun@samsung.com>