i40iw: Implement get_vector_affinity API

Storage ULPs (like NVMEoF) benefit from exposing affinity mapping
per completion vector to find the optimal multi-queue affinity
assignments. The ULPs call the verbs API ib_get_vector_affinity
introduced in commit c66cd353 ("RDMA/core: expose affinity mappings per
completion vector") to get the underlying devices affinity mappings.

Add support in driver to expose the affinity masks per MSI-X
completion vector.

Signed-off-by: Shiraz Saleem <shiraz.saleem@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>