niu: Determine the # of ports from the card's VPD data

Determine the number of physical ports from the card's VPD data.
Previous fix failed on Maramba platform which doesn't have the
"board-model" property. This fix uses the "model" property which
exists on all cards and Neptune based motherboards.

cstyle cleanup included.

Signed-off-by: Matheos Worku <matheos.worku@sun.com>
Signed-off-by: David S. Miller <davem@davemloft.net>