initial review - MFP / 802.11w groundwork

hi!

I'm pushing forward on MFP / 802.11w again because there's renewed
interest in WPA3 support and MFP is a pre-requisite.

I've got a set of diffs which implement some basic configuration bits
and stuff to handle the IGTK key slots (4 and 5) which currently just
throw an ioctl error from wpa_supplicant.

The diff stack is here - https://reviews.freebsd.org/D48172 .

It's part of a larger stack of diffs I'm using locally in my
development (which includes the channel representation stuff), but
they're effectively separate things. The MFP stuff is labelled as
such. As of the time of this mailing there's eight MFP related diffs
before the channel representation diff.

Everything in the review list should be a glorified "no-op" for
everyone else but it cleans things up enough to start deploying the
new key slots and types.

I'd appreciate some reviews here. Notably this doesn't magically make
MFP work or even be negotiated - I have a diff in my tree that
implements the in progress hacks to negotiate it for further
testing/development and it's on top of this particular diff.

Thanks!


-adrian