fcoe: Use CHECKSUM_PARTIAL to indicate CRC offload

When setting up CRC offload set ip_summed to CHECKSUM_PARTIAL
instead of CHECKSUM_UNNECESSARY. This is consistent with the
definition of CHECKSUM_PARTIAL.

The only driver that seems to be advertising NETIF_F_FCOE_CRC is
ixgbe. AFICT the driver does not look at ip_summed for FCOE and
just assumes that CRC is being offloaded.
Signed-off-by: Tom Herbert <tom@herbertland.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/scsi/fcoe/fcoe.c

@@ -1625,7 +1625,7 @@ static int fcoe_xmit(struct fc_lport *lport, struct fc_frame *fp)
 
 	/* crc offload */
 	if (likely(lport->crc_offload)) {
-		skb->ip_summed = CHECKSUM_UNNECESSARY;
+		skb->ip_summed = CHECKSUM_PARTIAL;
 		skb->csum_start = skb_headroom(skb);
 		skb->csum_offset = skb->len;
 		crc = 0;