net: arc_emac: don't pass multicast packets to kernel in non-multicast mode

The patch disable capturing multicast packets when multicast mode
disabled for ethernet ('ifconfig eth0 -multicast'). In that case
no multicast packet will be passed to kernel.

Signed-off-by: Alexander Kochetkov <al.kochet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>