btrfs: allow inline data extents creation if block size < page size

Previously inline data extents creation was disabled if the block size
(previously called sector size) is smaller than the page size, for the
following reasons:

- Possible mixed inline and regular data extents
  However this is also the same if the block size matches the page size,
  thus we do not treat mixed inline and regular extents as an error.

  And the chance to cause mixed inline and regular data extents are not
  even increased, it has the same requirement (compressed inline data
  extent covering the whole first block, followed by regular extents).

- Inability to handle async/inline delalloc range for block size < page
  size cases
  This is already fixed since commit 1d2fbb7f ("btrfs: allow
  compression even if the range is not page aligned").

  This was the major technical obstacle, but it's not anymore.

With that removed, we can enable inline data extents creation no matter
the block size nor the page size, allowing btrfs to have the same
capacity for all block sizes.

Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>