Merge r252230:

  Implement ifconfig_wlanX="HOSTAP".

  Not only this is a bit cleaner, it allows multiple instances of hostapd to be
  running on the system host, useful for simultaneous dual-band WiFi.
  This is similar to ifconfig_wlanX="WPA" but it uses /etc/hostapd-wlanX.conf.
  Compatibility with hostapd_enable=YES/NO was kept.