- Use ieee80211_probe_resp_alloc() to setup probe response template.

- Use ieee80211_probe_resp_alloc() to setup probe response template.
- Check the return value of ieee80211_probe_resp_alloc() and
  ieee80211_beacon_alloc().  Since these two functions use MB_DONTWAIT
  to allocate mbuf, it is quite possible they will return NULL.
- Turn on IEEE80211_FC0_VERSION_0 when setup null data and probe request
  templates as what we do in netproto/802_11.
- Don't transmit probe responses injected by netproto/802_11 layer,
  firmware will handle them for us.
- Move acx100's TIM ie template setup into common templates initialization
  routine, so acx111 will get its TIM ie template properly set up.
  This makes firmware add well formatted TIM ies to the end of the beacons
  instead of junked ones.
  Reported-by: Marcus Glocker <mglocker@openbsd.org>
- Obey DTIM period set in netproto/802_11, i.e. use ieee80211com.ic_dtim_period
- Reduce the length of Partial Virtual Bitmap in TIM template.