btrfs/246: skip the test if the tested btrfs doesn't support inline extents creation

btrfs/246: skip the test if the tested btrfs doesn't support inline extents creation

[FALSE ALERT]
If test case btrfs/246 is executed with a 16K page sized system (like
some aarch64 SoCs) using 4K sector size (would be the new default), the
test case would fail with output mismatch:

  btrfs/246 1s ... - output mismatch (see ~/xfstests-dev/results//btrfs/246.out.bad)
      --- tests/btrfs/246.out	2022-11-24 19:53:53.158470844 +0800
      +++ ~/xfstests-dev/results//btrfs/246.out.bad	2023-03-22 13:27:34.975796048 +0800
      @@ -3,3 +3,5 @@
       0ca3bfdeda1ef5036bfa5dad078a9f15724e79cf296bd4388cf786bfaf4195d0  SCRATCH_MNT/foobar
       sha256sum after mount cycle
       0ca3bfdeda1ef5036bfa5dad078a9f15724e79cf296bd4388cf786bfaf4195d0  SCRATCH_MNT/foobar
      +no inline extent found
      +no compressed extent found
      ...
      (Run 'diff -u ~/xfstests-dev/tests/btrfs/246.out ~/xfstests-dev/results//btrfs/246.out.bad'  to see the entire diff)

[CAUSE]
For current btrfs subpage support, there are still some limitations:

- No compressed write if the range is not fully page aligned
- No inline extents creation
  Reading inline extents is still supported

Thus we won't create such inlined compressed extent at all.

[FIX]
Just skip the test case if we can not even create a regular inline
extent.

This is done by a new require helper,
_require_btrfs_inline_extent_creation(), which would detect if btrfs can
even create an uncompressed inlined extent.

Reported-by: Hector Martin <marcan@marcan.st>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Neal Gompa <neal@gompa.dev>
Signed-off-by: Zorro Lang <zlang@kernel.org>