Fix bug when server recvs duplicate observe req
Fix bug when server recvs duplicate observe req

Change-Id: Ie6fc0ec0babaea45ca90352207df8794a5fe8468
Signed-off-by: Kishen Maloor <c62ddea3cd661a9268bff15f07fc2229cdc9ac02@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/26309
Tested-by: IoTivity Jenkins <6267f6022d49a8a37a7fe97da24aebfab797522c@iotivity.org>

iotivity/iotivity-constrained,iotivity/iotivity-constrained,iotivity/iotivity-constrained,iotivity/iotivity-constrained