netxen: cleanup mac list on driver unload

This fixes a tiny memory leak when driver is unloaded. The mac
address list maintained in netxen_adapter needs to deleted when
driver is going down.

Signed-off-by: Dhananjay Phadke <dhananjay@netxen.com>
Signed-off-by: David S. Miller <davem@davemloft.net>