Added missing DTLS #ifdef guard.
Added missing DTLS #ifdef guard.

One of the functions only used for DTLS was missing #ifdef guards
resulting in compile warnings.

Change-Id: Ieb0082e1dba2547e8d73d0526cf0aab3bf3af589
Signed-off-by: Jon A. Cruz <d4ae605477945a543a3ecda8955c93978db16a84@osg.samsung.com>
Signed-off-by: Sachin Agrawal <e527dde4abdf871552470c254efd4939572046d8@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/1333
Tested-by: jenkins-iotivity <09cb29e8a2b473a2c978382eec13ee06fa017bda@opendaylight.org>

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