geneve: cleanup hard coded value for Ethernet header length

Use ETH_HLEN instead and introduce two new macros: GENEVE_IPV4_HLEN
and GENEVE_IPV6_HLEN that include Ethernet header length, corresponded
IP header length and GENEVE_BASE_HLEN.
Signed-off-by: Alexey Kodanev <alexey.kodanev@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/geneve.c

@@ -36,6 +36,8 @@ MODULE_PARM_DESC(log_ecn_error, "Log packets received with corrupted ECN");
 
 #define GENEVE_VER 0
 #define GENEVE_BASE_HLEN (sizeof(struct udphdr) + sizeof(struct genevehdr))
+#define GENEVE_IPV4_HLEN (ETH_HLEN + sizeof(struct iphdr) + GENEVE_BASE_HLEN)
+#define GENEVE_IPV6_HLEN (ETH_HLEN + sizeof(struct ipv6hdr) + GENEVE_BASE_HLEN)
 
 /* per-network namespace private data for this module */
 struct geneve_net {
@@ -826,8 +828,8 @@ static int geneve_xmit_skb(struct sk_buff *skb, struct net_device *dev,
 		return PTR_ERR(rt);
 
 	if (skb_dst(skb)) {
-		int mtu = dst_mtu(&rt->dst) - sizeof(struct iphdr) -
-			  GENEVE_BASE_HLEN - info->options_len - 14;
+		int mtu = dst_mtu(&rt->dst) - GENEVE_IPV4_HLEN -
+			  info->options_len;
 
 		skb_dst_update_pmtu(skb, mtu);
 	}
@@ -872,8 +874,7 @@ static int geneve6_xmit_skb(struct sk_buff *skb, struct net_device *dev,
 		return PTR_ERR(dst);
 
 	if (skb_dst(skb)) {
-		int mtu = dst_mtu(dst) - sizeof(struct ipv6hdr) -
-			  GENEVE_BASE_HLEN - info->options_len - 14;
+		int mtu = dst_mtu(dst) - GENEVE_IPV6_HLEN - info->options_len;
 
 		skb_dst_update_pmtu(skb, mtu);
 	}