openbsd_wlan (and FreeBSD ieee80211_ioctl.h): Initial ioctl compatibility.

* Introduce IEEE80211_IOCTLS_ABBREVIATED to FreeBSD's ieee80211_ioctl.h,
so that the FreeBSD header can be included along with the OpenBSD
net80211 stack without triggering lots of errors, so we can use
these structs in openbsd_wlan ieee80211_haiku.cpp.

* Implement basic ieee80211req handling machinery. We aren't going
to handle anything but SIOCG80211 and SIOCS80211 in this method,
so we can simplify it a bit at the same time.

* Implement IEEE80211_IOC_SCAN_RESULTS to return scan results from
the OpenBSD WiFi stack in FreeBSD ioctl format.

This change adds two minor "features" (noted with #ifdefs) to the
OpenBSD net80211 stack: one to specify what node index to return
when returning known nodes (scan results), as this way we do not
have to allocate a huge buffer to store the scan results in before
sending them back to userland, but can instead get and convert
a single one at a time.

(We store the converted values in kernel mode all at once, though,
so this is not as efficient as it could be. More improvement possible.)

* Implement IEEE80211_IOC_BSSID and IEEE80211_IOC_SSID while we are at it.
This actually may make joining open networks possible, but I didn't
really test it. (They are used with SIOCG80211 to see what network
the device is currently connecting/connected to.)

openbsd_wlan: Basic adaptations to the net80211 layer.

The stack now compiles and links. Combining this with adaptations to
the driver gets things to the point where it runs scans, but we do
not yet implement ioctls so they can be returned to userland.

openbsd_wlan: Import OpenBSD net80211 layer and base dependencies.

Not yet wired into the build, of course.