EX-7683 utils: update handling of compr level for lz4

EX-7683 utils: update handling of compr level for lz4

The way lz4 compression level or acceleration factor is handled needs
to be adapted in order to match what is provided by the lz4 userspace
tool:
- any level between 0 and 2 is interpreted as the default lz4
  acceleration factor of 1;
- any level from 3 and up to 16 is interpreted as a compression level
  for internal lz4hc. Increasing the compression level trades CPU
  time for improved compression ratio;
- acceleration factor can be specified for the lz4fast compression
  type, from 1 to 26. This acceleration factor trades compression
  ratio for faster speed.

Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: I4711217c1a6601f29f78d262567da5998f657fc9
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/51380
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>