[PATCH] forcedeth: fix random memory scribbling bug

Two critical bugs were found in forcedeth 0.47:
 - TSO doesn't work.
 - pci_map_single() for the rx buffers is called with size==0.  This bug
   is critical, it causes random memory corruptions on systems with an
   iommu.

Below is a minimal fix for both bugs, for 2.6.15.

TSO will be fixed properly in the next version.  Tested on x86-64.

Signed-Off-By: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>