net: thunderbolt: Convert to use SPDX identifier

This gets rid of the licence boilerblate in favor of SPDX identifier
which only takes a single line comment.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/thunderbolt.c

@@ -1,14 +1,11 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Networking over Thunderbolt cable using Apple ThunderboltIP protocol
  *
  * Copyright (C) 2017, Intel Corporation
  * Authors: Amir Levy <amir.jer.levy@intel.com>
  *          Michael Jamet <michael.jamet@intel.com>
  *          Mika Westerberg <mika.westerberg@linux.intel.com>
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
  */
 
 #include <linux/atomic.h>