- Add noise floor in ieee80211_nodestats; return it as zero until we can

- Add noise floor in ieee80211_nodestats; return it as zero until we can
  update the api's so the driver can provide noise floor data
- Add a bandaid so IEEE80211_IOC_STA_STATS works for sta mode; when all
  nodes are in the station table this will no longer be needed
- Fix braino in IEEE80211_IOC_STA_INFO implementation; was supposed to
  take a MAC address and return info for that sta or all stations if
  ff:ff:ff:ff:ff was supplied -- but somehow this didn't get implemented;
  implement the intended semantics

Obtained-from: FreeBSD (sam@freebsd.org)

# NOTE: The RSSI statistics in ieee80211_nodestats is still unsigned