[IOT-839] Ensure correct map size when serializing rep payload

[IOT-839] Ensure correct map size when serializing rep payload

type & interface map size was hardcoded as two, which broke representation
deserialization when only one of type or interface was present.

Change-Id: I8356fc4ae80f649163d093adbac3cae49cac1cff
Signed-off-by: Erkka Kääriä <erkka.kaaria@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/4265
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Erich Keane <erich.keane@intel.com>
Reviewed-by: Jon A. Cruz <jonc@osg.samsung.com>