virtio: add VIRTIO_CONFIG_S_NEEDS_RESET device status bit

The VIRTIO 1.0 specification added the DEVICE_NEEDS_RESET device status
bit in "VIRTIO-98: Add DEVICE_NEEDS_RESET".  This patch defines the
device status bit in the uapi header file so that both the kernel and
userspace applications can use it.

The bit is currently unused by the virtio guest drivers and vhost.
According to the spec "a good implementation will try to recover by
issuing a reset".  This is not attempted here because it requires
auditing the virtio drivers to ensure there are no resource leaks or
crashes if the device needs to be reset mid-operation.

See "2.1 Device Status Field" in the VIRTIO 1.0 specification for
details.
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

include/uapi/linux/virtio_config.h

@@ -40,6 +40,8 @@
 #define VIRTIO_CONFIG_S_DRIVER_OK	4
 /* Driver has finished configuring features */
 #define VIRTIO_CONFIG_S_FEATURES_OK	8
+/* Device entered invalid state, driver must reset it */
+#define VIRTIO_CONFIG_S_NEEDS_RESET	0x40
 /* We've given up on this device. */
 #define VIRTIO_CONFIG_S_FAILED		0x80