enic: Fix build without _HAVE_ARCH_IPV6_CSUM

From: Scott Feldman <[email protected]>

On architectures (such as powerpc) that don't define _HAVE_ARCH_IPV6_CSUM, the enic compile fails with

drivers/net/enic/enic_main.c: In function 'enic_queue_wq_skb_tso':
drivers/net/enic/enic_main.c:575: error: implicit declaration of function 'csum_ipv6_magic'

Fix this by including <net/ip6_checksum.h>

---
Jeff, this is part of a patch Scott sent a while ago
(https://kerneltrap.org/mailarchive/linux-netdev/2008/9/20/3350614/thread)
that seems to have gotten dropped. Please apply.

 drivers/net/enic/enic_main.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

index f3a47a8..80119c9 100644
@@ -35,6 +35,8 @@
 #include <linux/ipv6.h>
 #include <linux/tcp.h>
 
+#include <net/ip6_checksum.h>
+
 #include "cq_enet_desc.h"
 #include "vnic_dev.h"
 #include "vnic_intr.h"

From: Roland Dreier <[email protected]>
Date: Mon, 13 Oct 2008 13:35:22 -0700

I already received a fix for this seperately in my tree from Kamalesh Babulal.