iwm - DragonFly modifications and a bug fix

iwm - DragonFly modifications and a bug fix

* Modifications to make iwm build for DragonFly.

* Fix a serious bug, iwm_stop_device() must clear the rxq stat
  data primarily to reset to hw rx ring index to 0.  Otherwise
  all packets already handled from 0 to the current hw rx ring index
  will be reprocessed on restart.

* Implement iwmsleep() instead of using msleep().  iwmsleep() will
  handle exiting and re-entering the wlan_serializer.  Without this
  we can easily deadlock on the double lock.

* Implement Makefile infrastructure.

* Revert the FreeBSD patch to remove the per-debvice netif, since our
  802.11 infrastructure has not yet been updated for that.

* Purge the ifq on start if the interface is not running.

* Misc other DragonFly adjustments.