btrfs: make sure btrfs can create compressed inline extent

btrfs: make sure btrfs can create compressed inline extent

Btrfs has the ability to inline small file extents into its metadata,
and such inlined extents can be further compressed if needed.

The new test case is for a regression caused by commit f2165627319f
("btrfs: compression: don't try to compress if we don't have enough
pages").

That commit prevents btrfs from creating compressed inline extents, even
"-o compress,max_inline=2048" is specified, only uncompressed inline
extents can be created.

The test case will make sure that the content of the small file is
consistent between cycle mount, then use "btrfs inspect dump-tree" to
verify the created extent is both inlined and compressed.

The regression is fixed by commit 4e9655763b82 ("Revert "btrfs:
compression: don't try to compress if we don't have enough pages"")

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