Creating rxe device on top of vlan interface will create a non-functional
device that has an empty gids table and can't be used for rdma cm
communication.

This is caused by the logic in
enum_all_gids_of_dev_cb()/is_eth_port_of_netdev(), which only considers
networks connected to "upper devices" of the configured network device,
resulting in an empty set of gids for a vlan interface, and attempts to
connect via this rdma device fail in cm_init_av_for_response because no
gids can be resolved.

Apparently, this behavior was implemented to fit the HW-RoCE devices that
create RoCE device per port, therefore RXE must behave the same like
HW-RoCE devices and create rxe device per real device only.

In order to communicate via a vlan interface, the user must use the gid
index of the vlan address instead of creating rxe over vlan.

Link: https://lore.kernel.org/r/20200811150415.3693-1-goody698@gmail.comSigned-off-by: Mohammad Heib <goody698@gmail.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>