fixed the bug related to coap over tcp pdu creation.

fixed the bug related to coap over tcp pdu creation.

The first nibble of the frame is used to indecate the length of
the options/payload. and if a value is 13, an 8-bit unsigned integer
follows the initial byte and indicates the length of options/payload
minus 13. even in case the length of options/payload is 13, an 8-bit
unsigned interger has to be used to indicate 0.

Change-Id: I580e126755ae4b3018fe7eb11eae34035b0efa6c
Signed-off-by: hyuna0213.jo <hyuna0213.jo@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/5901
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Jee Hyeok Kim <jihyeok13.kim@samsung.com>
(cherry picked from commit 417ac656bad3f3c84f5cbbc8a4c88b5426a4fe1d)
Reviewed-on: https://gerrit.iotivity.org/gerrit/5999
Reviewed-by: Jon A. Cruz <jon@joncruz.org>