btrfs: autodefrag with regular and hole extents

btrfs: autodefrag with regular and hole extents

In v5.11~v5.15 kernels, there is a regression in autodefrag that if
a cluster (up to 256K in size) has even a single hole, the whole
cluster will be rejected.

This will greatly reduce the efficiency of autodefrag.

The behavior is fixed in v5.16 by a full rework, although the rework
itself has other problems, it at least solves the problem.

Here we add a test case to reproduce the case, where we have a 128K
cluster, the first half is fragmented extents which can be
defragged.  The second half is hole.

Make sure autodefrag can defrag the 64K part.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>