ucast/mcast/mgmt HT rate.
- Init global ieee80211_htrateset only once; neither ic_htcaps nor
ic_txstream is changed when device is attached;
- Move global ieee80211_htrateset structure to ieee80211com;
there was a possible data race when more than 1 wireless device is
used simultaneously;
- Discard unsupported rates in ieee80211_ioctl_settxparams(); otherwise,
an unsupported value may break connectivity (actually,
'ifconfig wlan0 ucastrate 8' for RTL8188EU results in immediate
disconnect + infinite 'device timeout's after it).
Tested with:
- Intel 6205, STA mode.
- RTL8821AU, STA mode.
Reviewed by: adrian
Differential Revision: https://reviews.freebsd.org/D9871