rtw89: fix incorrect channel info during scan

We used to fill in rx skbs' frequency field by mac80211's current
channel value. In some cases, mac80211 switches channel before all
rx packets have been processed. This results in incorrect bss info.
We fix this by filling in frequency field with channel index obtained
from hardware, then fix potential cck missing issue by skb's original
hw rate. After all fix is done, convert hw rate back to the supported
band rate index.

Signed-off-by: Po Hao Huang <phhuang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20211111023706.14154-3-pkshih@realtek.com