* Add a new method to control NIC poweron / network-sleep / power off;
* Add in A-MPDU TX negotiation support, but comment it out because it
does break TX traffic;
* blank out the tx buffer before sending a firmware message, just in case;
* go into network-sleep once associated;
TODO:
* figure out why ampdu negotiation isn't working and breaking TX traffic,
then enable it.
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