RDMA/ipoib: Set rtnl_link_ops for ipoib interfaces

Report the "ipoib pkey", "mode" and "umcast" netlink attributes for every
IPoiB interface type, not just children created with 'ip link add'.

After setting the rtnl_link_ops for the parent interface, implement the
dellink() callback to block users from trying to remove it.

Fixes: 862096a8 ("IB/ipoib: Add more rtnl_link_ops callbacks")
Link: https://lore.kernel.org/r/20201004132948.26669-1-kamalheib1@gmail.com


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