rtw89: add 6G support to rate adaptive mechanism

Construct rate mask of 6G band, and rate adaptive mechanism can work well
on this band.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220211075953.40421-5-pkshih@realtek.com