SH-4163 Run an initial series of 'B' tests on the mesh downloader code

Bleh, had some old initialization code in place that meant I was using
32 connections.  (Always verify with 'netstat'...)  Logic is now to
use 1/4 of MeshMaxConncurrentRequests to head in the direction of 8
at a time.  Full count is used to implement a high-water level keeping
llcorehttp in work.