[NET]: IPV6 checksum offloading in network devices

The existing model for checksum offload does not correctly handle
devices that can offload IPV4 and IPV6 only. The NETIF_F_HW_CSUM flag
implies device can do any arbitrary protocol.

This patch:
 * adds NETIF_F_IPV6_CSUM for those devices
 * fixes bnx2 and tg3 devices that need it
 * add NETIF_F_IPV6_CSUM to ipv6 output (incl GSO)
 * fixes assumptions about NETIF_F_ALL_CSUM in nat
 * adjusts bridge union of checksumming computation

Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/bnx2.c b/drivers/net/bnx2.c
index ce3ed67..0f4f76f 100644
--- a/drivers/net/bnx2.c
+++ b/drivers/net/bnx2.c
@@ -6490,10 +6490,10 @@
 	memcpy(dev->perm_addr, bp->mac_addr, 6);
 	bp->name = board_info[ent->driver_data].name;
 
+	dev->features |= NETIF_F_IP_CSUM | NETIF_F_SG;
 	if (CHIP_NUM(bp) == CHIP_NUM_5709)
-		dev->features |= NETIF_F_HW_CSUM | NETIF_F_SG;
-	else
-		dev->features |= NETIF_F_IP_CSUM | NETIF_F_SG;
+		dev->features |= NETIF_F_IPV6_CSUM;
+
 #ifdef BCM_VLAN
 	dev->features |= NETIF_F_HW_VLAN_TX | NETIF_F_HW_VLAN_RX;
 #endif