alpha: fix broken network checksum

alpha: fix broken network checksum

The patch 2457d966ca51d61c57daaa310b83c049b586685c breaks networking on
alpha (there is a follow-up fix 5d1701cfe208409d51234408a06b4aaf46c2259f,
but networking is still broken even with the second patch).

The patch 2457d966ca51d61c57daaa310b83c049b586685c makes
csum_partial_copy_from_user check the pointer with access_ok. However,
csum_partial_copy_from_user is called also from csum_partial_copy_nocheck
and csum_partial_copy_nocheck is called on kernel pointers and it is
supposed not to check pointer validity.

This bug results in ssh session hangs if the system is loaded and bulk
data are printed to ssh terminal.

This patch fixes csum_partial_copy_nocheck to call set_fs(KERNEL_DS), so
that access_ok in csum_partial_copy_from_user accepts kernel-space
addresses.

Cc: stable@vger.kernel.org
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Matt Turner <mattst88@gmail.com>