Btrfs: write_buf is now callable outside send.c

Developing service cmds needs it.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
diff --git a/fs/btrfs/send.h b/fs/btrfs/send.h
index 9934e94..1bf4f32 100644
--- a/fs/btrfs/send.h
+++ b/fs/btrfs/send.h
@@ -130,4 +130,5 @@
 
 #ifdef __KERNEL__
 long btrfs_ioctl_send(struct file *mnt_file, void __user *arg);
+int write_buf(struct file *filp, const void *buf, u32 len, loff_t *off);
 #endif