mlx4_ib: set user mr attributes in struct ib_mr

Setting iova, length, and page_size allows this information to be
seen via NLDEV netlink queries, which can aid in user rdma debugging.

Signed-off-by: Steve Wise <swise@opengridcomputing.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>