net: virtio: use eth_hw_addr_set()

Commit 406f42fa0d ("net-next: When a bond have a massive amount
of VLANs...") introduced a rbtree for faster Ethernet address look
up. To maintain netdev->dev_addr in this tree we need to make all
the writes to it go through appropriate helpers.

Even though the current code uses dev->addr_len the we can switch
to eth_hw_addr_set() instead of dev_addr_set(). The netdev is
always allocated by alloc_etherdev_mq() and there are at least two
places which assume Ethernet address:
 - the line below calling eth_hw_addr_random()
 - virtnet_set_mac_address() -> eth_commit_mac_addr_change()

Acked-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20211027152012.3393077-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/virtio_net.c

@@ -3177,12 +3177,16 @@ static int virtnet_probe(struct virtio_device *vdev)
 	dev->max_mtu = MAX_MTU;
 
 	/* Configuration may specify what MAC to use.  Otherwise random. */
-	if (virtio_has_feature(vdev, VIRTIO_NET_F_MAC))
+	if (virtio_has_feature(vdev, VIRTIO_NET_F_MAC)) {
+		u8 addr[ETH_ALEN];
+
 		virtio_cread_bytes(vdev,
 				   offsetof(struct virtio_net_config, mac),
-				   dev->dev_addr, dev->addr_len);
-	else
+				   addr, ETH_ALEN);
+		eth_hw_addr_set(dev, addr);
+	} else {
 		eth_hw_addr_random(dev);
+	}
 
 	/* Set up our device-specific information */
 	vi = netdev_priv(dev);