bwn(4) updates - PHY-N support, newer firmware, etc

[Adrian Chadd]

Hi,

I've fixed RX RSSI calculatinos for PHY-G, PHY-LP and PHY-N hardware.
The noise/rssi is now valid, and so now net80211/wpa_supplicant makes
sane(r) AP selection decisions.

I've also done the firmware API 5xx support. That seems to work enough
to tinker with.



-adrian