batman-adv: use ETH_HLEN instead of sizeof(struct ethhdr)

Instead of using sizeof(struct ethhdr) it is strongly recommended to use the
kernel macro ETH_HLEN. This patch substitute each occurrence of the former
expressione with the latter one.

Signed-off-by: Antonio Quartulli <ordex@autistici.org>
diff --git a/net/batman-adv/vis.c b/net/batman-adv/vis.c
index c4a5b8c..cec216f 100644
--- a/net/batman-adv/vis.c
+++ b/net/batman-adv/vis.c
@@ -434,12 +434,12 @@
 		return NULL;
 
 	info->skb_packet = dev_alloc_skb(sizeof(*packet) + vis_info_len +
-					 sizeof(struct ethhdr));
+					 ETH_HLEN);
 	if (!info->skb_packet) {
 		kfree(info);
 		return NULL;
 	}
-	skb_reserve(info->skb_packet, sizeof(struct ethhdr));
+	skb_reserve(info->skb_packet, ETH_HLEN);
 	packet = (struct vis_packet *)skb_put(info->skb_packet, sizeof(*packet)
 					      + vis_info_len);
 
@@ -894,11 +894,11 @@
 
 	bat_priv->my_vis_info->skb_packet = dev_alloc_skb(sizeof(*packet) +
 							  MAX_VIS_PACKET_SIZE +
-							 sizeof(struct ethhdr));
+							  ETH_HLEN);
 	if (!bat_priv->my_vis_info->skb_packet)
 		goto free_info;
 
-	skb_reserve(bat_priv->my_vis_info->skb_packet, sizeof(struct ethhdr));
+	skb_reserve(bat_priv->my_vis_info->skb_packet, ETH_HLEN);
 	packet = (struct vis_packet *)skb_put(bat_priv->my_vis_info->skb_packet,
 					      sizeof(*packet));