RDMA/core: Set gid_attr.ndev for iWARP devices

Have the iwarp side properly set the ndev in the device's sgid_attrs
so that address resolution can treat it more like a RoCE device.

Link: https://lore.kernel.org/r/168960673933.3007.8043081822081877578.stgit@manet.1015granger.net
Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Tom Talpey <tom@talpey.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>