tg3: Automatically size stat/test string arrays

This patch reimplements the size preprocessor constants of the stats and
ethtool test string arrays.  The size is calculated at compile time
rather than using static constants.

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