RDMA/cma: Use correct address when leaving multicast group

In RoCE we should use cma_iboe_set_mgid() and not cma_set_mgid to generate
the mgid, otherwise we will generate an IGMP for an incorrect address.

Fixes: b5de0c60 ("RDMA/cma: Fix use after free race in roce multicast join")
Link: https://lore.kernel.org/r/913bc6783fd7a95fe71ad9454e01653ee6fb4a9a.1642491047.git.leonro@nvidia.com


Signed-off-by: Maor Gottlieb <maorg@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>