Fix MHI driver kernel panic with bridged/LAN traffic

[Copilot]

MHI driver v1.3.8-r3 crashes when LAN cable is connected during active cellular data transfer. Root cause: aggressive WARN_ON() calls flood kernel log when non-QMAP packets arrive via bridge/LAN, triggering system instability.

Changes

driver/quectel_MHI/src/devices/mhi_netdev_quectel.c

• Add NULL check in ndev_to_mhi() - Prevent dereference when unexpected device pointers arrive from bridge stack
• Remove WARN_ON for protocol mismatch - Non-QMAP packets are normal for bridged traffic, pass through silently
• Remove WARN_ON for NULL mhi_netdev - Expected when non-MHI packets arrive, handle gracefully

static struct mhi_netdev *ndev_to_mhi(struct net_device *ndev) {
	struct mhi_netdev_priv *mhi_netdev_priv;

	if (!ndev)
		return NULL;

	mhi_netdev_priv = netdev_priv(ndev);
	return mhi_netdev_priv->mhi_netdev;
}

if (skb->protocol != htons(ETH_P_MAP)) {
	/* Not a QMAP packet, may be bridged/LAN traffic */
	return RX_HANDLER_PASS;
}

The rx_handler registration with NULL (for HyFi compatibility) remains unchanged. This fix handles the resulting edge cases without warnings.

Testing

Requires validation on RM520N-GL module with immortalwrt 25.12, cellular data active + LAN connected.

Original prompt

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This section details on the original issue you should resolve

<issue_title>[BUG]MHI1.3.8-r3版本只要网线使用蜂窝数据无限重启</issue_title>
<issue_description>设备：西瓜皮v3（遇到其他设备的人同样出现此问题，5G模块相同）
OS：immortalwrt25.12
5G模块：RM520N-GL
只要网线插入lan口使用，瞬间设备重启，日志都没有。
使用MHI1.3.8-r1就不会出现此问题。
</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [BUG]MHI1.3.8-r3版本只要网线使用蜂窝数据无限重启 #150

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