sky2: large memory workaround.

This patch might fix problems with 4G or more of memory.
It stops the driver from doing a small optimization for Tx and Rx,
and instead always sets the high-page on tx/rx descriptors.

Fixes-bug: http://bugzilla.kernel.org/show_bug.cgi?id=9725

Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>