RDMA/rtrs-clt: Cap max_io_size

Max io size is limited by both remote buffer size and the max fr pages per
mr.

Link: https://lore.kernel.org/r/20210325153308.1214057-20-gi-oh.kim@ionos.com


Signed-off-by: Jack Wang <jinpu.wang@ionos.com>
Reviewed-by: Md Haris Iqbal <haris.iqbal@ionos.com>
Signed-off-by: Gioh Kim <gi-oh.kim@ionos.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>