RFR: CollectedHeap::max_tlab_size is measured in words

[Aleksey Shipilev]

http://cr.openjdk.java.net/~shade/shenandoah/tlab-max-word/webrev.01/

We mistakenly report byte size in max_tlab_size, which wrecks up TLAB sizing policies.

Testing: tier3_gc_shenandoah, eyeballing TLAB stats

Thanks,
-Aleksey