RDMA/core: Remove query_pkey from the mandatory ops

The query_pkey() isn't mandatory for the iwarp providers, so remove this
requirement from the RDMA core.

Link: https://lore.kernel.org/r/20200714183414.61069-4-kamalheib1@gmail.com


Signed-off-by: Kamal Heib <kamalheib1@gmail.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>