net: usb: lan78xx: Add .ndo_features_check

As reported by Eric Dumazet, there are still some outstanding
cases where the driver does not handle TSO correctly when skb's
are over a certain size. Most cases have been fixed, this patch
should ensure that forwarded SKB's that are greater than
MAX_SINGLE_PACKET_SIZE - TX_OVERHEAD are software segmented
and handled correctly.
Signed-off-by: James Hughes <james.hughes@raspberrypi.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/usb/lan78xx.c

@@ -20,6 +20,7 @@
 #include <linux/mdio.h>
 #include <linux/phy.h>
 #include <net/ip6_checksum.h>
+#include <net/vxlan.h>
 #include <linux/interrupt.h>
 #include <linux/irqdomain.h>
 #include <linux/irq.h>
@@ -3668,6 +3669,19 @@ static void lan78xx_tx_timeout(struct net_device *net)
 	tasklet_schedule(&dev->bh);
 }
 
+static netdev_features_t lan78xx_features_check(struct sk_buff *skb,
+						struct net_device *netdev,
+						netdev_features_t features)
+{
+	if (skb->len + TX_OVERHEAD > MAX_SINGLE_PACKET_SIZE)
+		features &= ~NETIF_F_GSO_MASK;
+
+	features = vlan_features_check(skb, features);
+	features = vxlan_features_check(skb, features);
+
+	return features;
+}
+
 static const struct net_device_ops lan78xx_netdev_ops = {
 	.ndo_open		= lan78xx_open,
 	.ndo_stop		= lan78xx_stop,
@@ -3681,6 +3695,7 @@ static const struct net_device_ops lan78xx_netdev_ops = {
 	.ndo_set_features	= lan78xx_set_features,
 	.ndo_vlan_rx_add_vid	= lan78xx_vlan_rx_add_vid,
 	.ndo_vlan_rx_kill_vid	= lan78xx_vlan_rx_kill_vid,
+	.ndo_features_check	= lan78xx_features_check,
 };
 
 static void lan78xx_stat_monitor(struct timer_list *t)