virtio: teach virtio_has_feature() about transport features

Drivers don't add transport features to their table, so we
shouldn't check these with virtio_check_driver_offered_feature().

We could perhaps add an ->offered_feature() virtio_config_op,
but that perhaps that would be overkill for a consitency check
like this.
Signed-off-by: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

include/linux/virtio_config.h

@@ -113,7 +113,9 @@ static inline bool virtio_has_feature(const struct virtio_device *vdev,
 	if (__builtin_constant_p(fbit))
 		BUILD_BUG_ON(fbit >= 32);
 
-	virtio_check_driver_offered_feature(vdev, fbit);
+	if (fbit < VIRTIO_TRANSPORT_F_START)
+		virtio_check_driver_offered_feature(vdev, fbit);
+
 	return test_bit(fbit, vdev->features);
 }