driver: ipvlan: Remove useless member mtu_adj of struct ipvl_dev

The mtu_adj is initialized to zero when alloc mem, there is no any
assignment to mtu_adj. It is only used in ipvlan_adjust_mtu as one
right value.
So it is useless member of struct ipvl_dev, then remove it.
Signed-off-by: NGao Feng <fgao@ikuai8.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ipvlan/ipvlan.h

@@ -73,7 +73,6 @@ struct ipvl_dev {
 	DECLARE_BITMAP(mac_filters, IPVLAN_MAC_FILTER_SIZE);
 	netdev_features_t	sfeatures;
 	u32			msg_enable;
-	u16			mtu_adj;
 };
 
 struct ipvl_addr {

drivers/net/ipvlan/ipvlan_main.c

@@ -32,7 +32,7 @@ static const struct l3mdev_ops ipvl_l3mdev_ops = {
 
 static void ipvlan_adjust_mtu(struct ipvl_dev *ipvlan, struct net_device *dev)
 {
-	ipvlan->dev->mtu = dev->mtu - ipvlan->mtu_adj;
+	ipvlan->dev->mtu = dev->mtu;
 }
 
 static int ipvlan_register_nf_hook(void)