Roaming mode can change value into 'firm mode' and disable.
Authentication mode can change into 'Open System authentication'
and 'Shared Key Authentication' with Prism2 chip.
wi_get_id() was introduced in order that chip might judge automatically
whether it is Prism2 chip. Therefore, a pp_prism2 entry in
"struct wi_pcmcia_product" became unnecessary.
ichiro