[LinuxCNC/linuxcnc Issue#294] rtapi real time task never runs on system with HT disabled in BIOS

IRC user itx> reports a system where, with HT disabled, NPROCESSORS_ONLN is 2, and the default affinity mask is 0x5.

Since uspace rtapi tries to bind to (NPROCESSORSONLN-1), i.e., CPU 1 in this case, the realtime task never runs.

(The kernel is 4.9-rt from debian stretch repository. unreported whether it’s 32- or 64-bit)