export virtio_rng.h

Hello Rusty,

The entropy device was added after we exported all virtio headers. This
patch adds virtio_rng.h to the exportable userspace headers.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/include/linux/Kbuild b/include/linux/Kbuild
index a26f565..327f606 100644
--- a/include/linux/Kbuild
+++ b/include/linux/Kbuild
@@ -356,6 +356,7 @@
 unifdef-y += virtio_console.h
 unifdef-y += virtio_pci.h
 unifdef-y += virtio_ring.h
+unifdef-y += virtio_rng.h
 unifdef-y += vt.h
 unifdef-y += wait.h
 unifdef-y += wanrouter.h