Thread count should default to *ONLINE* CPU count

[staticglobal]

Background:
In apputils.c we have get_system_number_of_cpus() which returns sysconf(_SC_NPROCESSORS_CONF)); (number of "configured" processors) and get_system_active_number_of_cpus() which returns sysconf(_SC_NPROCESSORS_ONLN); (number of "online/available" processors)

Then mainrelay.c sets turn_params.cpus to get_system_number_of_cpus() (capped at 128) and then also defaults general_relay_servers_number to this value.

Issue:
On most systems in most situations configured == online so the difference is meaningless. However, when running in some virtualized environments, the difference can be significant.

In one scenario when running under HyperV a VM configured for 2 CPUs, the hardware always reports a total of 240 total CPUs, with only the first 2 CPUs being online and the other 238 offline. Presumably this is how the host implements virtualized CPU hotplugging. From dmesg:

[    0.033154] smpboot: Allowing 240 CPUs, 238 hotplug CPUs

And getconf:

localhost ~ # getconf _NPROCESSORS_CONF
240
localhost ~ # getconf _NPROCESSORS_ONLN
2

coturn correctly logs both the total (capped) and enabled CPU counts

0: (2341): INFO: System cpu num is 128
0: (2341): INFO: System enable num is 2

...but then proceeds with setting up 128 worker threads despite the system only having 2 CPUs. I believe this behavior is incorrect and instead turn_params.cpus should be set from get_system_active_number_of_cpus() instead.

[jonesmz]

This seems like a good improvement to me.

Have you considered making a PR to change it in the way you suggested?