Fix for DTLS message failure when previous not closed properly

Fix for DTLS message failure when previous not closed properly

This fixes JIRA issue IOT-417.  When a previous DTLS session was not
properly closed, DTLS messaging would fail.  This patch ensures that
DTLS sessions are properly closed.

Change-Id: I0483253cad313c7596ae30d9624db57c072417d8
Signed-off-by: jnashok <jn.ashok@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/889
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Sachin Agrawal <sachin.agrawal@intel.com>