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: Import OpenBSD net80211 layer and base dependencies.

Not yet wired into the build, of course.