UDS: check connection state better

UDS: check connection state better

Select(2)ing on UNIX domain sockets was not working properly because
connection state wasn't properly checked/propagated. So selecting for
a read descriptor and closing the write descriptor on the other end
didn't cause select to return. Similarly, read(2) kept blocking while
it should return an error when the other end closed the socket.

Change-Id: I3f5bb52af1a6b03313d508bf915fc838357ba450