wifi: mt76: mt7996: fix RX buffer size of MCU event

wifi: mt76: mt7996: fix RX buffer size of MCU event

Some management frames are first processed by the firmware and then
passed to the driver through the MCU event rings. In CONNAC3, event rings
do not support scatter-gather and have a size limitation of 2048 bytes.
If a packet sized between 1728 and 2048 bytes arrives from an event ring,
the ring will hang because the driver attempts to use scatter-gather to
process it.

To fix this, include the size of struct skb_shared_info in the MCU RX
buffer size to prevent scatter-gather from being used for event skb in
mt76_dma_rx_fill_buf().

Fixes: 98686cd21624 ("wifi: mt76: mt7996: add driver for MediaTek Wi-Fi 7 (802.11be) devices")
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/20250515032952.1653494-7-shayne.chen@mediatek.com
Signed-off-by: Felix Fietkau <nbd@nbd.name>