tg3: Disable TSS also during tg3_close()

The TSS flag needs to be turned off during tg3_close().  If the device
fails to allocate more than one MSI-X vector the next time the device is
brought up, transmits will fail.

Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>