wifi: mt76: mt7996: fix MLO set key and group key issues

wifi: mt76: mt7996: fix MLO set key and group key issues

This patch fixes the following key issues:
- Pass correct link BSS to mt7996_mcu_add_key(), and use HW beacon
  protection mode for mt7990 chipset
- Do not do group key deletion for GTK and IGTK due to FW design, the
  delete key command will delete all group keys of a link BSS
- For deleting BIGTK, FW adds a new flow, but the "sec->add" field
  should be filled with "SET_KEY". Note that if BIGTK is not deleted, it
  will cause beacon decryption issue when switching from an AP interface
  to a station interface

Fixes: 0c45d52276fd ("wifi: mt76: mt7996: fix setting beacon protection keys")
Co-developed-by: Allen Ye <allen.ye@mediatek.com>
Signed-off-by: Allen Ye <allen.ye@mediatek.com>
Co-developed-by: Peter Chiu <chui-hao.chiu@mediatek.com>
Signed-off-by: Peter Chiu <chui-hao.chiu@mediatek.com>
Signed-off-by: Shayne Chen <shayne.chen@mediatek.com>
Link: https://patch.msgid.link/20251106064203.1000505-10-shayne.chen@mediatek.com
Signed-off-by: Felix Fietkau <nbd@nbd.name>