netxen: hw multicast filtering

Enable multicast address filtering capabilities in the hardware.
Upto 16 multicast addresses can be programmed for each physical
port. Support "allmulti" mode, if enabled.

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