IB/ipoib: Make sendonly multicast joins create the mcast group

Since IPoIB should, as much as possible, emulate how multicast
sends work on Ethernet for regular TCP/IP apps, there should be
no requirement to subscribe to a multicast group before your
sends are properly sent.  However, due to the difference in how
multicast is handled on InfiniBand, we must join the appropriate
multicast group before we can send to it.  Previously we tried
not to trigger the auto-create feature of the subnet manager when
doing this because we didn't have tracking of these sendonly
groups and the auto-creation might never get undone.  The previous
patch added timing to these sendonly joins and allows us to
leave them after a reasonable idle expiration time.  So supply
all of the information needed to auto-create group.

Signed-off-by: Doug Ledford <dledford@redhat.com>