include/hw/virtio: document some more usage of notifiers

Lets document some more of the core VirtIODevice structure.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20230710153522.3469097-7-alex.bennee@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

include/hw/virtio/virtio.h

@@ -150,10 +150,18 @@ struct VirtIODevice
     VMChangeStateEntry *vmstate;
     char *bus_name;
     uint8_t device_endian;
+    /**
+     * @user_guest_notifier_mask: gate usage of ->guest_notifier_mask() callback.
+     * This is used to suppress the masking of guest updates for
+     * vhost-user devices which are asynchronous by design.
+     */
     bool use_guest_notifier_mask;
     AddressSpace *dma_as;
     QLIST_HEAD(, VirtQueue) *vector_queues;
     QTAILQ_ENTRY(VirtIODevice) next;
+    /**
+     * @config_notifier: the event notifier that handles config events
+     */
     EventNotifier config_notifier;
     bool device_iotlb_enabled;
 };