[ofw] [owf][patch] user multicast offload support

[Fab Tillier]

>>Voltaire has developed the LSP for Multicast Offload. Fast data path
>>will use this service provider working on IB using ibal.dll.
>>Original service provider TCP/IPoIB is using to transfer IGMP requests
>>to Ethernet routers which may be connected to IB host through IPR.
>>IB join will come from user mode and from IPoIB too. The common place
>>for them is in the ibal.lib.
>>To improve performance of HCA on receive path, IPoIB does not issue
>>ATTACH to the group which already attached from user mode by LSP.
>
>This leads me back to my original suggestion of simply having a
>parameter on the join multicast group that indicates if the QP should be
>attached.  This is way simpler and moves the complexity of determining
>when to attach to the ULP, where it belongs.

Even better us to let the client apps use the existing ib_join/leave_mcast functions and internally detect whether the SA MC registration needs to be done or not, as well as reference counting the SA MC registration.

Would you ever join a MC group without also attaching at least one QP?

-Fab