Onload will act in accordance with RFC 791 when it comes to the IP_MULTICAST_TTL setting. Using Onload, if IP_MULTICAST_TTL=0, packets will never be transmitted on the wire.
This differs from the Linux kernel where the following behavior has been observed:
Kernel - IP_MULTICAST_TTL 0 - if there is a local listener, packets will not be transmitted on the wire.
Kernel - IP_MULTICAST_TTL 0 - if there is NO local listener, packets will always be transmitted on the wire.