niu: Fix probing regression for maramba on-board chips.

Changeset 7f7c4072 ("niu: Determine
the # of ports from the card's VPD data") caused maramba on-board
NIU ports to stop probing properly.

The old code had a fallback that would use a num_ports value of
4 if all the probing methods failed, but that was removed.

This restores the fallback of 4 ports, to get things working
again.

Bump driver version and release date.

Signed-off-by: David S. Miller <davem@davemloft.net>