virtio: update the comments for transport features

The existing comments for transport features are outdated.
So update them to address the latest changes in the spec.
Suggested-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NTiwei Bie <tiwei.bie@intel.com>
Reviewed-by: NCornelia Huck <cohuck@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>

include/uapi/linux/virtio_config.h

@@ -45,9 +45,12 @@
 /* We've given up on this device. */
 #define VIRTIO_CONFIG_S_FAILED		0x80
 
-/* Some virtio feature bits (currently bits 28 through 32) are reserved for the
- * transport being used (eg. virtio_ring), the rest are per-device feature
- * bits. */
+/*
+ * Virtio feature bits VIRTIO_TRANSPORT_F_START through
+ * VIRTIO_TRANSPORT_F_END are reserved for the transport
+ * being used (e.g. virtio_ring, virtio_pci etc.), the
+ * rest are per-device feature bits.
+ */
 #define VIRTIO_TRANSPORT_F_START	28
 #define VIRTIO_TRANSPORT_F_END		38