i dont know if this works but man ifconfig does magic..
[-]allmulti
Enable or disable all-multicast mode. If selected, all multicast packets on the network will be received by
the interface.
multicast
Set the multicast flag on the interface. This should not normally be needed as the drivers set the flag cor-
rectly themselves.
these two options are pasted from man ifconfig
try it...
and tell us...