Undo r195846 for now - allow raw frame transmit in monitor mode.

The original commit was supposed to stop the ability to do raw frame
injection in monitor mode to arbitrary channels (whether supported
by regulatory or not) however it doesn't seem to have been followed
by any useful way of doing it.

Apparently AHDEMO is supposed to be that way, but it seems to require
too much fiddly things (disable scanning, set a garbage SSID, etc)
for it to actually be useful for spoofing things.

So for now let's just disable it and instead look to filter transmit
in the output path if the channel isn't allowed by regulatory.
That way monitor RX works fine but TX will be blocked.

I don't plan on MFC'ing this to -10 until the regulatory enforcement
bits are written.