i40e: Add UDP segmentation offload support

Based on a series from Alexander Duyck this change adds UDP segmentation
offload support to the i40e driver.

CC: Alexander Duyck <alexander.h.duyck@intel.com>
CC: Willem de Bruijn <willemb@google.com>
Signed-off-by: Josh Hunt <johunt@akamai.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/i40e/i40e_main.c

@@ -12931,6 +12931,7 @@ static int i40e_config_netdev(struct i40e_vsi *vsi)
 			  NETIF_F_GSO_IPXIP6		|
 			  NETIF_F_GSO_UDP_TUNNEL	|
 			  NETIF_F_GSO_UDP_TUNNEL_CSUM	|
+			  NETIF_F_GSO_UDP_L4		|
 			  NETIF_F_SCTP_CRC		|
 			  NETIF_F_RXHASH		|
 			  NETIF_F_RXCSUM		|

drivers/net/ethernet/intel/i40e/i40e_txrx.c

@@ -2960,10 +2960,16 @@ static int i40e_tso(struct i40e_tx_buffer *first, u8 *hdr_len,
 
 	/* remove payload length from inner checksum */
 	paylen = skb->len - l4_offset;
-	csum_replace_by_diff(&l4.tcp->check, (__force __wsum)htonl(paylen));
 
-	/* compute length of segmentation header */
-	*hdr_len = (l4.tcp->doff * 4) + l4_offset;
+	if (skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4) {
+		csum_replace_by_diff(&l4.udp->check, (__force __wsum)htonl(paylen));
+		/* compute length of segmentation header */
+		*hdr_len = sizeof(*l4.udp) + l4_offset;
+	} else {
+		csum_replace_by_diff(&l4.tcp->check, (__force __wsum)htonl(paylen));
+		/* compute length of segmentation header */
+		*hdr_len = (l4.tcp->doff * 4) + l4_offset;
+	}
 
 	/* pull values out of skb_shinfo */
 	gso_size = skb_shinfo(skb)->gso_size;