net: fix cpu_max_bits_warn() usage in netif_attrmask_next{,_and}

The functions require to be passed with a cpu index prior to one that is
the first to start search, so the valid input range is [-1, nr_cpu_ids-1).
However, the code checks against [-1, nr_cpu_ids).

Acked-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Yury Norov <yury.norov@gmail.com>