MFC: statistics fixups:

MFC: statistics fixups:
    o change rssi to be signed in ieee80211_nodestats
    o add noise floor in ieee80211_nodestats (use an implicit hole to
      preserve layout); return it as zero until we can update the api's
      so the driver can provide noise floor data
    o 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
    o 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 and leave a compat shim at the old
      ioctl number for the previous api

Note this changes the api for IEEE80211_IOC_STA_INFO but old binaries
will continue to work.  FreeBSD_version bumped so apps can track the
change (no such applications are known to exist but just in case).