smb: client: compress: LZ77 code improvements cleanup

- Check data compressibility with some heuristics (copied from
  btrfs):
  - should_compress() final decision is is_compressible(data)

- Cleanup compress/lz77.h leaving only lz77_compress() exposed:
  - Move parts to compress/lz77.c, while removing the rest of it
    because they were either unused, used only once, were
    implemented wrong (thanks to David Howells for the help)

- Updated the compression parameters (still compatible with
  Windows implementation) trading off ~20% compression ratio
  for ~40% performance:
  - min match len: 3 -> 4
  - max distance: 8KiB -> 1KiB
  - hash table type: u32 * -> u64 *

Known bugs:
This implementation currently works fine in general, but breaks with
some payloads used during testing.  Investigation ongoing, to be
fixed in a next commit.

Signed-off-by: Enzo Matsumiya <[email protected]>
Co-developed-by: David Howells <[email protected]>
Signed-off-by: David Howells <[email protected]>
Signed-off-by: Steve French <[email protected]>

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