btrfs: replace GPL boilerplate by SPDX -- headers

Remove GPL boilerplate text (long, short, one-line) and keep the rest,
ie. personal, company or original source copyright statements. Add the
SPDX header.

Unify the include protection macros to match the file names.

Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/send.h b/fs/btrfs/send.h
index 3aa4bc5..ead397f 100644
--- a/fs/btrfs/send.h
+++ b/fs/btrfs/send.h
@@ -1,22 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2012 Alexander Block.  All rights reserved.
  * Copyright (C) 2012 STRATO.  All rights reserved.
- *
- * This program is free software; you can redistribute it and/or
- * modify it under the terms of the GNU General Public
- * License v2 as published by the Free Software Foundation.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
- * General Public License for more details.
- *
- * You should have received a copy of the GNU General Public
- * License along with this program; if not, write to the
- * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
- * Boston, MA 021110-1307, USA.
  */
 
+#ifndef BTRFS_SEND_H
+#define BTRFS_SEND_H
+
 #include "ctree.h"
 
 #define BTRFS_SEND_STREAM_MAGIC "btrfs-stream"
@@ -132,3 +122,5 @@ enum {
 #ifdef __KERNEL__
 long btrfs_ioctl_send(struct file *mnt_file, struct btrfs_ioctl_send_args *arg);
 #endif
+
+#endif