Added code to send close_notify alert when OC stack shuts down.
Added code to send close_notify alert when OC stack shuts down.

When peers receive close_notify alert they clean up the DTLS
session state.

Change-Id: I56efabc3d73a428406cd0c1d5796f762d57f5089
Signed-off-by: Sachin Agrawal <e527dde4abdf871552470c254efd4939572046d8@intel.com>

iotivity/iotivity,tienfuc/iotivity-democlient-snap,tienfuc/iotivity-democlient-snap,WojciechLuczkow/iotivity,santais/iotivity,santais/iotivity_1.1.0,santais/iotivity_1.1.0,santais/iotivity,santais/iotivity_1.1.0,tienfuc/iotivity-democlient-snap,tienfuc/iotivity-democlient-snap,santais/iotivity_1.1,iotivity/iotivity,rzr/iotivity,rzr/iotivity,WojciechLuczkow/iotivity,WojciechLuczkow/iotivity,WojciechLuczkow/iotivity,santais/iotivity,WojciechLuczkow/iotivity,iotivity/iotivity,iotivity/iotivity,santais/iotivity_1.1,santais/iotivity_1.1,kartben/iotivity,WojciechLuczkow/iotivity,rzr/iotivity,rzr/iotivity,santais/iotivity,kartben/iotivity,kartben/iotivity,rzr/iotivity,santais/iotivity,WojciechLuczkow/iotivity,santais/iotivity_1.1.0,kartben/iotivity,iotivity/iotivity,kartben/iotivity,kartben/iotivity,santais/iotivity_1.1.0,kartben/iotivity,tienfuc/iotivity-democlient-snap,iotivity/iotivity,santais/iotivity_1.1,santais/iotivity_1.1,tienfuc/iotivity-democlient-snap,tienfuc/iotivity-democlient-snap,santais/iotivity,santais/iotivity_1.1,WojciechLuczkow/iotivity,rzr/iotivity,rzr/iotivity,santais/iotivity_1.1,tienfuc/iotivity-democlient-snap,tienfuc/iotivity-democlient-snap,santais/iotivity_1.1.0,santais/iotivity_1.1.0,iotivity/iotivity,kartben/iotivity,iotivity/iotivity,santais/iotivity_1.1,tienfuc/iotivity-democlient-snap,santais/iotivity