vxlan: reduce dirty cache line in vxlan_find_mac

vxlan_find_mac() unconditionally set f->used for every packet,
this causes a cache miss for every packet, since remote, hlist
and used of vxlan_fdb share the same cache line, which are
accessed when send every packets.

so f->used is set only if not equal to jiffies, to reduce dirty
cache line times, this gives 3% speed-up with small packets.
Signed-off-by: Zhang Yu <zhangyu31@baidu.com>
Signed-off-by: Li RongQing <lirongqing@baidu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/vxlan.c

@@ -464,7 +464,7 @@ static struct vxlan_fdb *vxlan_find_mac(struct vxlan_dev *vxlan,
 	struct vxlan_fdb *f;
 
 	f = __vxlan_find_mac(vxlan, mac, vni);
-	if (f)
+	if (f && f->used != jiffies)
 		f->used = jiffies;
 
 	return f;