tg3: Fix 5906 transmit hangs

tg3: Fix 5906 transmit hangs

This is a resubmit backport of commit 92c6b8d16a36df3f28b2537bed2a56491fb08f11
to kernel version 2.6.32. The gentoo bug report can be found at
https://bugs.gentoo.org/show_bug.cgi?id=301091. Thanks to Matt Carlson for his
assistance and working me to fix a regression caused by the initial patch.  The
original description is as follows:

The 5906 has trouble with fragments that are less than 8 bytes in size.  This
patch works around the problem by pivoting the 5906's transmit routine to
tg3_start_xmit_dma_bug() and introducing a new SHORT_DMA_BUG flag that enables
code to detect and react to the problematic condition.

Signed-off-by: Mike Pagano <mpagano@gentoo.org>
Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>