vdpa net: follow VirtIO initialization properly at cvq isolation probing

This patch solves a few issues.  The most obvious is that the feature
set was done previous to ACKNOWLEDGE | DRIVER status bit set.  Current
vdpa devices are permissive with this, but it is better to follow the
standard.

Fixes: 152128d ("vdpa: move CVQ isolation check to net_init_vhost_vdpa")
Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
Message-Id: <20230915170836.3078172-4-eperezma@redhat.com>
Tested-by: Lei Yang <leiyang@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

net/vhost-vdpa.c

@@ -1345,8 +1345,7 @@ static int vhost_vdpa_probe_cvq_isolation(int device_fd, uint64_t features,
     uint64_t backend_features;
     int64_t cvq_group;
     uint8_t status = VIRTIO_CONFIG_S_ACKNOWLEDGE |
-                     VIRTIO_CONFIG_S_DRIVER |
-                     VIRTIO_CONFIG_S_FEATURES_OK;
+                     VIRTIO_CONFIG_S_DRIVER;
     int r;
 
     ERRP_GUARD();
@@ -1361,15 +1360,22 @@ static int vhost_vdpa_probe_cvq_isolation(int device_fd, uint64_t features,
         return 0;
     }
 
+    r = ioctl(device_fd, VHOST_VDPA_SET_STATUS, &status);
+    if (unlikely(r)) {
+        error_setg_errno(errp, -r, "Cannot set device status");
+        goto out;
+    }
+
     r = ioctl(device_fd, VHOST_SET_FEATURES, &features);
     if (unlikely(r)) {
-        error_setg_errno(errp, errno, "Cannot set features");
+        error_setg_errno(errp, -r, "Cannot set features");
         goto out;
     }
 
+    status |= VIRTIO_CONFIG_S_FEATURES_OK;
     r = ioctl(device_fd, VHOST_VDPA_SET_STATUS, &status);
     if (unlikely(r)) {
-        error_setg_errno(errp, -r, "Cannot set status");
+        error_setg_errno(errp, -r, "Cannot set device status");
         goto out;
     }