Remove empty stubs for detach/attach_mcast

Just use ibv_cmd_* directly.  Simplifies the code and fixes const
correctness warnings due to changes in libibverbs.

Signed-off-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>
3 files changed