add the prefix definition to resolve the build error

add the prefix definition to resolve the build error

after '[IOT-828] OCRepresentation to provide host info' was submitted,
build error has been encountered while building WITH_TCP=true option.
so I added the prefix definition for coap over tcp.

Change-Id: Ia479a1946eae78beffc146b61f99ec864bd0b142
Signed-off-by: hyuna0213.jo <hyuna0213.jo@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/4371
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Jaehong Jo <jaehong.jo@samsung.com>
Reviewed-by: Jon A. Cruz <jonc@osg.samsung.com>