net: devres: define a separate devres structure for devm_alloc_etherdev()

Not using a proxy structure to store struct net_device doesn't save
anything in terms of compiled code size or memory usage but significantly
decreases the readability of the code with all the pointer casting.

Define struct net_device_devres and use it in devm_alloc_etherdev_mqs().
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/devres.c

@@ -7,30 +7,34 @@
 #include <linux/etherdevice.h>
 #include <linux/netdevice.h>
 
-static void devm_free_netdev(struct device *dev, void *res)
+struct net_device_devres {
+	struct net_device *ndev;
+};
+
+static void devm_free_netdev(struct device *dev, void *this)
 {
-	free_netdev(*(struct net_device **)res);
+	struct net_device_devres *res = this;
+
+	free_netdev(res->ndev);
 }
 
 struct net_device *devm_alloc_etherdev_mqs(struct device *dev, int sizeof_priv,
 					   unsigned int txqs, unsigned int rxqs)
 {
-	struct net_device **dr;
-	struct net_device *netdev;
+	struct net_device_devres *dr;
 
 	dr = devres_alloc(devm_free_netdev, sizeof(*dr), GFP_KERNEL);
 	if (!dr)
 		return NULL;
 
-	netdev = alloc_etherdev_mqs(sizeof_priv, txqs, rxqs);
-	if (!netdev) {
+	dr->ndev = alloc_etherdev_mqs(sizeof_priv, txqs, rxqs);
+	if (!dr->ndev) {
 		devres_free(dr);
 		return NULL;
 	}
 
-	*dr = netdev;
 	devres_add(dev, dr);
 
-	return netdev;
+	return dr->ndev;
 }
 EXPORT_SYMBOL(devm_alloc_etherdev_mqs);