btrfs-tools: upgrade 6.0 -> 6.0.1

Changelog:
==========
* send: minor speed up for v2 due to increased buffer size
* resize: invalid command line options fail with error code
* quota rescan:
   * add long options --status and --wait
   * new option to wait but don't start rescan
* qgroup show: print path by default, updated format
* qgroup: new subcommand clear-stale, remove qgroups without their subvolumes
* experimental:
   * add warnings to commands that have it enabled (mkfs, image, btrfstune)
* other:
   * documentation, help text, error message updates

Signed-off-by: Wang Mingyu <wangmy@fujitsu.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>