"device" test slightly improved

When testing device for BUS protocol it checks whether message
is delivered to the original sender.

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>
Bug in uni-directional sockets fixed

SNDFD and RCVFD objects were sometimes unsignaled even when they
were not created (as the socket was uni-directional).

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>