RX_FLAG_HT must be included when reporting MCS rates. Without
this, mac80211 ended up dropping any frame sent at MCS index 12
or higher and that resulted in oddly random looking errors in
mac80211_hwsim tests.

Signed-off-by: Jouni Malinen <j@w1.fi>
Signed-off-by: John W. Linville <linville@tuxdriver.com>