sky2: size status ring based on Tx/Rx ring

Sky2 status ring must be big enough to handle worst case number
of status messages. It was being oversized (to handle dual port cards),
and excessive number of tx ring entries were allowed. This patch reduces
the footprint and makes sure the value is enough.

Later patch to add RSS increases the number of possible Rx status elements.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>