client: Report proper close reason

When we get a POLLHUP or VIR_EVENT_HANDLE_HANGUP event for a client, we
still want to read from the socket to process any accumulated data. But
doing so inevitably results in an error and a call to
virNetClientMarkClose before we get to processing the hangup event (and
another call to virNetClientMarkClose). However the close reason passed
to the second virNetClientMarkClose call is ignored because another one
was already set. We need to pass the correct close reason when marking
the socket to be closed for the first time.

https://bugzilla.redhat.com/show_bug.cgi?id=1373859



Signed-off-by: Jiri Denemark <jdenemar@redhat.com>