Okay here is the contorller based one...
you go to configuration-->ap group --->click edit on the ap group in which the aps are on --->profile --> wireless lan ---> Virtual APS
Here is a picture...
Now remeber you need to do it in all virtual APS you got... at least in my lab controller i got 4 virtual APs... so i put it to all of them... But well i dont need any multicast in my enviroment. Also check Convert Broadcast ARP requests to unicast
Also you will get a warning of Warning: broadcast-filter arp should be enabled with this option. Otherwise ARP requests will be dropped! So enable that before enabling this... you will see that option on advanced services on stateful firewall(which is on the left menu)