rmc_newclass does not reject negative priority: only checks upper bound, latent negative array index

Summary

rmc_newclass(int pri,...)(:201): only checks pri>=RM_MAXPRIO, not pri<0. Indexes ifd->active_[pri](:304), num_[pri](:331), alloc_[pri](:332) — RM_MAXPRIO(8) sized arrays. Negative pri -> negative array index OOB read/write. Currently unreachable: sole caller passes u_int8_t pre-checked CBQ_MAXPRI. API defense-in-depth.