Extend slh max size to avoid 0C4 ABENDs

[Pamazok]

Proposed changes

For some "content" the allocated SLH size (technically the number of blocks) is not enough, so ZSS thread is ABENDed with 0C4-4 like below:

SLH at 0x3FF90A50 cannot allocate above block size 16 > 0 mxbl 2 bkct 2 bksz 65535
httpserver: ABEND 0C4-04 averted when handling datasetContents

Technically we increased the number of max blocks, so we do not request a 2 times bigger buffer.
But it's enough for some cases.

Type of change

• Bug fix (non-breaking change which fixes an issue)

PR Checklist

• If the changes in this PR are meant for the next release / mainline, this PR targets the "staging" branch.
• My code follows the style guidelines of this project (see: Contributing guideline)

Testing

The bug was found by the "OMEGAMON for Storage" team and we verified that the issue solved with these changes.

[1000TurquoisePogs]

This was discussed on call last week and agreed to be a good change.
Thank you for the investigation and PR.