RDMA/siw,rxe: Make emulated devices virtual in the device tree

RDMA/siw,rxe: Make emulated devices virtual in the device tree

This moves siw and rxe to be virtual devices in the device tree:

lrwxrwxrwx 1 root root 0 Nov  6 13:55 /sys/class/infiniband/rxe0 -> ../../devices/virtual/infiniband/rxe0/

Previously they were trying to parent themselves to the physical device of
their attached netdev, which doesn't make alot of sense.

My hope is this will solve some weird syzkaller hits related to sysfs as
it could be possible that the parent of a netdev is another netdev, eg
under bonding or some other syzkaller found netdev configuration.

Nesting a ib_device under anything but a physical device is going to cause
inconsistencies in sysfs during destructions.

Link: https://lore.kernel.org/r/0-v1-dcbfc68c4b4a+d6-virtual_dev_jgg@nvidia.com
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>