netxen: mtu, mac, link status changes

MAC addr, multicast filters, mtu are set through firmware commands
in firmware v4.0.0+ because of virtualization of physical ports.
Link status is also read from registers allocated by firmware for
each virtual port.

Signed-off-by: Dhananjay Phadke <dhananjay@netxen.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>