Exclude private types from doxygen

Exclude private types from doxygen

Older doxygens document private types if definitions for them are outside of the outer class.
cond command is one way to prevent them from being documented.

Change-Id: I151180a0724eca6ecf8f5682cbcbab4ca5ee42e6
Signed-off-by: coderhyme <jhyo.kim@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/3477
Reviewed-by: Hun-je Yeon <hunje.yeon@samsung.com>
Reviewed-by: Madan Lanka <lanka.madan@samsung.com>
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Habib Virji <habib.virji@samsung.com>