commit 7932c0bd upstream.

While reviewing vhost log code, I found out that log_file is never
set. Note: I haven't tested the change (QEMU doesn't use LOG_FD yet).
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>