The FDB dump callback requires the related net_device so move it to the
struct switchdev_fdb_dump superset instead of using a callback param.

With this done, it'll be simpler to change the dump function signature.
Signed-off-by: NVivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>