Maximum number of threads is limited to 100

The number of routing threads in Maxscale is hard-coded to 100. This is starting to become something that could soon be exceeded on some of the larger machines that the cloud providers offer. For example the m5.24xlarge instance on AWS has 96 vCPUs and the new ARM instances (m6g.16xlarge) offer 64 cores.

Since there's no real reason to limit the number of cores if the system does indeed have more than 100 threads, the limit should be at some point either removed or at least doubled.