wifi: mt76: mt7996: add eht rx rate support

Add support to report eht rx rate.
Note that extended fields for eht in mt76_rx_status will make the struct
size exceed the cb size, so make nss and band share the same u8.

Signed-off-by: Shayne Chen <shayne.chen@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>