urtwn: first cut of 11n

[Adrian Chadd]

hiya,

Here's my first cut of 11n support for urtwn:

http://people.freebsd.org/~adrian/net80211/20160320-urtwn-11n-1.diff

notably:

* the rate table init is wrong - it only knows about legacy rates, not 11n rates
* there's no HT40 support
* there's no short-gi support
* there's no A-MPDU support, so TX throughput won't improve dramatically.
* the urtwn_tx_raw() path doesn't set the rate index or frame type at
all; I'm not sure what's going on there.
* not sure if I should set the 'mode' to 11GN if we're transmitting at
a rate that's not MCS (eg, if we are trying to transmit an 11b rate in
11bgn mode). I should double/triple check that.

I'm using it right now on:

Mar 20 20:01:47 gertrude kernel: urtwn0: <Realtek 802.11n NIC, class
0/0, rev 2.00/0.00, addr 5> on usbus0
Mar 20 20:01:47 gertrude kernel: urtwn0: MAC/BB RTL8188EU, RF 6052 1T1R
Mar 20 20:01:47 gertrude kernel: urtwn0: enabling 11n

I'd appreciate any feedback and maybe implement/testing the rest of it
and send it to me. :P

Thanks,


-adrian