Attempt to address Bug #176201 - don't advertise what the AP announced
to us. Instead, advertise what we can do based on what the AP says and what
we're capped at by the VAP settings.

For non-STA modes we still advertise what our VAP settings are.

It may be that I've over-complicated this and instead of capping things
we can just always announce what we're capable of. But this should at least
stop the blatantly wrong handling of A-MPDU parameters.

(I'll happily simplify things if someone can dig up a replacement, better
compliant behaviour.)

PR: kern/176201