vhost_net: examine pointer types during un-producing

After commit fc72d1d54dd9 ("tuntap: XDP transmission"), we can
actually queueing XDP pointers in the pointer ring, so we should
examine the pointer type before freeing the pointer.

Fixes: fc72d1d54dd9 ("tuntap: XDP transmission")
Reported-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 7433bb2..28cfa64 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -655,7 +655,7 @@ static struct tun_struct *tun_enable_queue(struct tun_file *tfile)
 	return tun;
 }
 
-static void tun_ptr_free(void *ptr)
+void tun_ptr_free(void *ptr)
 {
 	if (!ptr)
 		return;
@@ -667,6 +667,7 @@ static void tun_ptr_free(void *ptr)
 		__skb_array_destroy_skb(ptr);
 	}
 }
+EXPORT_SYMBOL_GPL(tun_ptr_free);
 
 static void tun_queue_purge(struct tun_file *tfile)
 {