xhttp: Add SPDX identifiers

src/modules/xhttp/xhttp_mod.c

@@ -3,6 +3,8 @@
  *
  * This file is part of Kamailio, a free SIP server.
  *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ *
  * Kamailio is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
  * the Free Software Foundation; either version 2 of the License, or

src/modules/xhttp/xhttp_trans.c

@@ -3,6 +3,8 @@
  *
  * This file is part of Kamailio, a free SIP server.
  *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ *
  * Kamailio is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
  * the Free Software Foundation; either version 2 of the License, or

src/modules/xhttp/xhttp_trans.h

@@ -3,6 +3,8 @@
  *
  * This file is part of Kamailio, a free SIP server.
  *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ *
  * Kamailio is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
  * the Free Software Foundation; either version 2 of the License, or