tg3: Add TSS support

This patch exposes the additional transmit rings to the kernel and makes
the necessary modifications to transmit, open, and close paths.

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