[NET]: IA64 checksum annotations and cleanups.

* sanitize prototypes, annotate
* ntohs -> shift in checksum calculations
* kill access_ok() in csum_partial_copy_from_user
* collapse do_csum_partial_copy_from_user

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>