vhost-user: Print unexpected slave message types

When we receive an unexpected message type on the slave fd, print
the type.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

hw/virtio/vhost-user.c

@@ -1061,7 +1061,7 @@ static void slave_read(void *opaque)
                                                           fd[0]);
         break;
     default:
-        error_report("Received unexpected msg type.");
+        error_report("Received unexpected msg type: %d.", hdr.request);
         ret = -EINVAL;
     }