Add a copyright and license statement for a radiotap header file

This file is a part of the radiotap parser that Andy Green agreed to
relicense under the BSD license (per email, 11 Aug 2007 07:42:05
+0100). The copyright/license statement was updated in radiotap.c,
but this radiotap_iter.h file was forgotten at that point.

src/utils/radiotap_iter.h

@@ -1,3 +1,18 @@
+/*
+ * Radiotap parser
+ *
+ * Copyright 2007		Andy Green <andy@warmcat.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.
+ *
+ * Alternatively, this software may be distributed under the terms of BSD
+ * license.
+ *
+ * See README and COPYING for more details.
+ */
+
 #ifndef __RADIOTAP_ITER_H
 #define __RADIOTAP_ITER_H