BUILD: SLE12: revert "graphdriver/btrfs: use kernel UAPI headers"

This reverts commit 3208dca.

On SLE 12, our UAPI headers are too old, resulting in us being unable to
build the btrfs driver with the new headers. This patch is only needed
for SLE-12.

Signed-off-by: Aleksa Sarai <[email protected]>

daemon/graphdriver/btrfs/btrfs.go

@@ -5,17 +5,12 @@ package btrfs // import "github.com/docker/docker/daemon/graphdriver/btrfs"
 
 /*
 #include <stdlib.h>
-#include <stdio.h>
 #include <dirent.h>
 
-#include <linux/version.h>
-#if LINUX_VERSION_CODE < KERNEL_VERSION(4,12,0)
-    #error "Headers from kernel >= 4.12 are required to build with Btrfs support."
-    #error "HINT: Set 'DOCKER_BUILDTAGS=exclude_graphdriver_btrfs' to build without Btrfs."
-#endif
-
-#include <linux/btrfs.h>
-#include <linux/btrfs_tree.h>
+// keep struct field name compatible with btrfs-progs < 6.1.
+#define max_referenced max_rfer
+#include <btrfs/ioctl.h>
+#include <btrfs/ctree.h>
 
 static void set_name_btrfs_ioctl_vol_args_v2(struct btrfs_ioctl_vol_args_v2* btrfs_struct, const char* value) {
     snprintf(btrfs_struct->name, BTRFS_SUBVOL_NAME_MAX, "%s", value);