There is no point in limiting the available priority range to 99 for
all classes but SCHED_COBALT, although we support up to 258 distinct
levels internally.

POSIX explicitly states that such limit is implementation-dependent,
and provides for sched_get_priority_max() for retrieving it
dynamically. Applications wary of portability between the Cobalt and
Mercury cores should probe for such limit.

All real-time classes exposed to userland now support up to 256 levels
[0..255], except SCHED_COBALT which gives access to the widest range
[0..257] available internally.