do not use kernel-internal macros in public header

src/libsystemd-bus/kdbus.h:337:2: error: enumerator value for 'KDBUS_NAME_IN_QUEUE' is not an integer constant
  KDBUS_NAME_IN_QUEUE   = BIT(16),
test: allow name_list() function to print full list of connected clients

It's a simple user space implementation of KDBUS_NAME_LIST_UNIQUE_NAMES
test: do not try to read "name", when none is attached