IB/core cleanup: Add const to RDMA helpers

The ib_device passed to the new RDMA helpers is constant.  Declare the
ib_device as const in the following functions.

rdma_protocol_ib
rdma_protocol_roce
rdma_protocol_iwarp
rdma_ib_or_roce
rdma_cap_ib_mad
rdma_cap_ib_smi
rdma_cap_ib_cm
rdma_cap_iw_cm
rdma_cap_ib_sa
rdma_cap_ib_mcast
rdma_cap_af_ib
rdma_cap_eth_ah

Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Hal Rosenstock <hal@mellanox.com>
Reviewed-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>