[PATCH] e1000: disable TSO on the 82544 with slab debugging

CONFIG_DEBUG_SLAB changes alignments of the data structures the slab
allocators return. These break certain workarounds for TSO on the 82544.
Since DEBUG_SLAB is relatively rare and not used for performance sensitive
cases, the simplest fix is to disable TSO in this special situation.

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>