Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Revert r208590. A license ack is not needed as per r186984.

Make the user ack the license before using this firmware.

MFC after: 3 days

Updates to the iwn driver:
* iwnfw has now been split into individual modules so autoloading of
firmware module(s) does work again.
* Changes have been made to RUN -> AUTH transition, this should fix the
issue reported by Glen and others.
* Brandon reported issues in iwn_cmd() with large commands, those have
been fixed to.
* DEAUTH is now handled correctly.

Submitted by: Bernhard Schmidt <bschmidt at techwires.net>