Ignored copyin return feeds uninitialized stack sched_param into ksched

Summary

sys_sched_setparam(:202) and sys_sched_setscheduler(:258) discard copyin() return. Fault -> uninitialized stack sched_param passed to ksched. Root-only (CAN_AFFECT uid==0 gate). Compare rr_get_interval(:348-349) which checks.