[ath] ath_rate_sample changes; please test

Hi,

I've just committed some changes to the ath_rate_sample module which
teach it the bare minimum to transmit MCS frames when in 11n mode.

No, this doesn't mean 11n mode is yet available or ready (there's some
further work in the TX path first.)

I'd appreciate some testing of this just to ensure I haven't busted legacy mode.

Thanks,


Adrian