vdpa: do not block migration if device has cvq and x-svq=on

It was a mistake to forbid in all cases, as SVQ is already able to send
all the CVQ messages before start forwarding data vqs.  It actually
caused a regression, making impossible to migrate device previously
migratable.

Fixes: 36e4647 ("vdpa: add vhost_vdpa_net_valid_svq_features")
Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
Message-Id: <20230602143854.1879091-2-eperezma@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Tested-by: Lei Yang <leiyang@redhat.com>

net/vhost-vdpa.c

@@ -915,13 +915,16 @@ static NetClientState *net_vhost_vdpa_init(NetClientState *peer,
         s->cvq_isolated = cvq_isolated;
 
         /*
-         * TODO: We cannot migrate devices with CVQ as there is no way to set
-         * the device state (MAC, MQ, etc) before starting the datapath.
+         * TODO: We cannot migrate devices with CVQ and no x-svq enabled as
+         * there is no way to set the device state (MAC, MQ, etc) before
+         * starting the datapath.
          *
          * Migration blocker ownership now belongs to s->vhost_vdpa.
          */
-        error_setg(&s->vhost_vdpa.migration_blocker,
-                   "net vdpa cannot migrate with CVQ feature");
+        if (!svq) {
+            error_setg(&s->vhost_vdpa.migration_blocker,
+                       "net vdpa cannot migrate with CVQ feature");
+        }
     }
     ret = vhost_vdpa_add(nc, (void *)&s->vhost_vdpa, queue_pair_index, nvqs);
     if (ret) {