Fix Doxm Handler for Manufacturer Cert OTM

Fix Doxm Handler for Manufacturer Cert OTM

Fix error due to confirmable cert OTM

Change-Id: Id191ae12e3842e910a44b9d025794caf6aaaf16b
Signed-off-by: Jongmin Choi <jminl.choi@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/15227
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Jongsung Lee <js126.lee@samsung.com>
Reviewed-by: Randeep Singh <randeep.s@samsung.com>
(cherry picked from commit 50a09e72b62edc9179fdc8b824a0cc6bfbeee88f)
Reviewed-on: https://gerrit.iotivity.org/gerrit/15311