IB/ipoib: Ignore L3 master device

IB/ipoib: Ignore L3 master device

Currently, all master upper netdevices (e.g., bond, VRF) are treated
equally.

When a VRF netdevice is used over an IPoIB netdevice, the expected
netdev resolution is on the lower IPoIB device which has the IP address
assigned to it and not the VRF device.

The rdma_cm module (CMA) tries to match incoming requests to a
particular netdevice. When successful, it also validates that the return
path points to the same device by performing a routing table lookup.
Currently, the former would resolve to the VRF netdevice, while the
latter to the correct lower IPoIB netdevice, leading to failure in
rdma_cm.

Improve this by ignoring the VRF master netdevice, if it exists, and
instead return the lower IPoIB device.

Signed-off-by: Vlad Dumitrescu <vdumitrescu@nvidia.com>
Reviewed-by: Parav Pandit <parav@nvidia.com>
Signed-off-by: Edward Srouji <edwards@nvidia.com>
Link: https://patch.msgid.link/20250916111103.84069-5-edwards@nvidia.com
Signed-off-by: Leon Romanovsky <leon@kernel.org>