RDMA/i40iw: Constify ops structs

The ops structs are never modified. Make them const to allow the compiler
to put them in read-only memory.

Link: https://lore.kernel.org/r/20201121002529.89148-1-rikard.falkeborn@gmail.com


Signed-off-by: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>