net: fix driver build errors due to missing net/ip6_checksum.h include

  2.6.27-git2 kernel build fails with allyesconfig on powerpc with 
build error 

<introduced by commit 01f2e4ea> 

CC    drivers/net/enic/enic_main.o
drivers/net/enic/enic_main.c: In function ‘enic_queue_wq_skb_tso’:
drivers/net/enic/enic_main.c:576: error: implicit declaration of function ‘csum_ipv6_magic’
make[3]: *** [drivers/net/enic/enic_main.o] Error 1

<introduced by commit c4e84bde>

drivers/net/qlge/qlge_main.c: In function ‘ql_tso’:
drivers/net/qlge/qlge_main.c:1862: error: implicit declaration of function ‘csum_ipv6_magic’
make[3]: *** [drivers/net/qlge/qlge_main.o] Error 1
  
<introduced by commit 95252236

>

drivers/net/jme.c: In function ‘jme_tx_tso’:
drivers/net/jme.c:1784: error: implicit declaration of function ‘csum_ipv6_magic’
make[2]: *** [drivers/net/jme.o] Error 1

Signed-off-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Signed-off-by: Ron Mercer <ron.mercer@qlogic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>