TG3: Disable TSO by default

Disable TSO by default on some chips due to hardware errata.

Enabling TSO can lead to tx timeouts in some cases when the TSO
header size exceeds 80 bytes on the affected chips.  This limit
can be exceeded when the TCP header contains the timestamp option
plus 2 SACK blocks, for example.  A more complete workaround is
available in the next 2.6.18 kernel.

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>