wifi: mt76: connac: rework connac helpers

Rework connac helpers related to rate and phymode.
This is a preliminary patch to add MLO support for mt7996 chipsets.

Co-developed-by: Bo Jiao <Bo.Jiao@mediatek.com>
Signed-off-by: Bo Jiao <Bo.Jiao@mediatek.com>
Signed-off-by: Shayne Chen <shayne.chen@mediatek.com>
Link: https://patch.msgid.link/20250102163508.52945-21-nbd@nbd.name


Signed-off-by: Felix Fietkau <nbd@nbd.name>