IB/mlx5: Listen to netdev register/unresiter events in switchdev mode

Currently we listen to netdev register/unregister event based on PCI
device. When in switchdev mode PF and representors share the same PCI
device, so in order to pair ib device and netdev in switchdev mode
compare the netdev that triggered the event to that of the representor.

Expose a function that lets you receive the netdev associated what
a given representor.

Signed-off-by: Mark Bloch <markb@mellanox.com>
Reviewed-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>