be2net: fix net-snmp error because of wrong packet stats

Wrong packet statistics for multicast Rx was causing net-snmp error messages
every 15 seconds. Instead of picking the multicast stats from hardware,
now maintain it in the driver itself.

Signed-off-by: Ajit Khaparde <ajitk@serverengines.com>
Signed-off-by: David S. Miller <davem@davemloft.net>