net/vlan: make a judgment before calling fuction

Make a judgment before calling fuction.

Signed-off-by: gaohedong <[email protected]>

Author: HedongGao

drivers/net/vlan.c

@@ -250,7 +250,10 @@ static void vlan_reclaim(FAR struct netdev_lowerhalf_s *dev)
   FAR struct vlan_device_s      *vlan = (FAR struct vlan_device_s *)dev;
   FAR struct netdev_lowerhalf_s *real = vlan->real;
 
-  real->ops->reclaim(real);
+  if (real->ops->reclaim)
+    {
+      real->ops->reclaim(real);
+    }
 }
 
 /****************************************************************************