net: switchdev: pass callback to dump operation

Similar to the notifier_call callback of a notifier_block, change the
function signature of switchdev dump operation to:

    int switchdev_port_obj_dump(struct net_device *dev,
                                enum switchdev_obj_id id, void *obj,
                                int (*cb)(void *obj));

This allows the caller to pass and expect back a specific
switchdev_obj_* structure instead of the generic switchdev_obj one.

Drivers implementation of dump operation can now expect this specific
structure and call the callback with it. Drivers have been changed
accordingly.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>