RDMA/rtrs-clt: Use rdma_event_msg in log

It's easier to understand a string instead of enum.

Link: https://lore.kernel.org/r/20210222141551.54345-2-jinpu.wang@cloud.ionos.com
Signed-off-by: Jack Wang <jinpu.wang@cloud.ionos.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>