tools/virtio: separate headers more.

This makes them a bit more like the kernel headers, so we can include more
real kernel headers in our tests.

In addition this means that we don't break tools/virtio with the next
patch.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/tools/virtio/linux/virtio_config.h b/tools/virtio/linux/virtio_config.h
new file mode 100644
index 0000000..5049967
--- /dev/null
+++ b/tools/virtio/linux/virtio_config.h
@@ -0,0 +1,6 @@
+#define VIRTIO_TRANSPORT_F_START	28
+#define VIRTIO_TRANSPORT_F_END		32
+
+#define virtio_has_feature(dev, feature) \
+	test_bit((feature), (dev)->features)
+