xfrm: interface: enable TSO on xfrm interfaces

Underlying xfrm output supports gso packets.
Declare support in hw_features and adapt the xmit MTU check to pass GSO
packets.
Signed-off-by: Eyal Birger <eyal.birger@gmail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/xfrm/xfrm_interface.c

@@ -296,7 +296,8 @@ xfrmi_xmit2(struct sk_buff *skb, struct net_device *dev, struct flowi *fl)
 	}
 
 	mtu = dst_mtu(dst);
-	if (skb->len > mtu) {
+	if ((!skb_is_gso(skb) && skb->len > mtu) ||
+	    (skb_is_gso(skb) && !skb_gso_validate_network_len(skb, mtu))) {
 		skb_dst_update_pmtu_no_confirm(skb, mtu);
 
 		if (skb->protocol == htons(ETH_P_IPV6)) {
@@ -564,6 +565,11 @@ static void xfrmi_dev_setup(struct net_device *dev)
 	eth_broadcast_addr(dev->broadcast);
 }
 
+#define XFRMI_FEATURES (NETIF_F_SG |		\
+			NETIF_F_FRAGLIST |	\
+			NETIF_F_GSO_SOFTWARE |	\
+			NETIF_F_HW_CSUM)
+
 static int xfrmi_dev_init(struct net_device *dev)
 {
 	struct xfrm_if *xi = netdev_priv(dev);
@@ -581,6 +587,8 @@ static int xfrmi_dev_init(struct net_device *dev)
 	}
 
 	dev->features |= NETIF_F_LLTX;
+	dev->features |= XFRMI_FEATURES;
+	dev->hw_features |= XFRMI_FEATURES;
 
 	if (phydev) {
 		dev->needed_headroom = phydev->needed_headroom;