RDMA: Constify the argument of the work request conversion functions

When posting a send work request, the work request that is posted is not
modified by any of the RDMA drivers. Make this explicit by constifying
most ib_send_wr pointers in RDMA transport drivers.

Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Steve Wise <swise@opengridcomputing.com>
Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/hw/mlx5/mlx5_ib.h

@@ -469,7 +469,7 @@ struct mlx5_umr_wr {
 	u32				mkey;
 };
 
-static inline struct mlx5_umr_wr *umr_wr(struct ib_send_wr *wr)
+static inline const struct mlx5_umr_wr *umr_wr(const struct ib_send_wr *wr)
 {
 	return container_of(wr, struct mlx5_umr_wr, wr);
 }