tg3: Move TSO_CAPABLE assignment

This patch moves the code that asserts the TSO_CAPABLE flag closer to
where the TSO capabilities flags are set.  There isn't a good enough
reason for the code to be separated.

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