rtw89: declare HE capabilities in 6G band

To work properly in 6G band, declare HE 6G capabilities. Without this fix,
it can only TX/RX with OFDM rates.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220307012741.6371-1-pkshih@realtek.com