[otus] enable 802.11n for 2GHz and 5GHz.

This flips on basic 11n for 2GHz/5GHz station operation.

• It flips on HT20 and MCS rates;
• It enables A-MPDU decap - the payload format is a bit different;
• It does do some basic checks for HT40 but I haven't yet flipped on HT40 support;
• It enables software A-MSDU transmit; I honestly don't want to make A-MPDU TX work and there are apparently issues with QoS and A-MPDU TX. So I totally am ignoring A-MPDU TX;
• MCS rate transmit is fine.

I haven't:

• A-MPDU TX, as I said above;
• made radiotap work fully;
• HT40;
• short-GI support;
• lots of other stuff that honestly no-one is likely to use.

But! Hey, this is another ye olde 11n USB NIC that now works pretty OK
in 11n rates. A-MPDU receive seems fine enough given it's a draft-n
device from before 2010.

Tested:

• Ye olde UB82 Test NIC (AR9170 + AR9104) - 2GHz/5GHz