be2net: support configuration of 64 multicast addresses instead of 32

To send upto 64 addresses in the multicast-set cmd, the non-embeeded cmd format
that provides for a bigger buffer is used instead of an embedded format.

Signed-off-by: Sathya Perla <sathyap@serverengines.com>
Signed-off-by: David S. Miller <davem@davemloft.net>