vhost-user-bridge: fix resume regression (since 2.9)

Commit e10e798c85 switched to libvhost-user which lacked support
for resuming the avail_idx based on used_idx.

Fixes:
https://bugzilla.redhat.com/show_bug.cgi?id=1485867

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

tests/vhost-user-bridge.c

@@ -466,11 +466,18 @@ vubr_panic(VuDev *dev, const char *msg)
     vubr->quit = 1;
 }
 
+static bool
+vubr_queue_is_processed_in_order(VuDev *dev, int qidx)
+{
+    return true;
+}
+
 static const VuDevIface vuiface = {
     .get_features = vubr_get_features,
     .set_features = vubr_set_features,
     .process_msg = vubr_process_msg,
     .queue_set_started = vubr_queue_set_started,
+    .queue_is_processed_in_order = vubr_queue_is_processed_in_order,
 };
 
 static void