Do a full HAL reset (cold) rather than a warm reset.

It seems some state isn't being cleared right and after a while the
chip stops being useful.

Saw this on ar9280/ar9285 APs. :(
add ipfw!
Support doing stuff to the wifi parent interface when it comes up.

The dir825b1 needs to setup a mac address manually for one of the
ath NICs.  This is just a hack to do that.

Ideally there'd be ath0/ath1 configuration chunks that would let us
do parent device specific setup.. I'll look at doing this soon.