net: dsa: use switchdev_obj_dump_cb_t everywhere

Now that the DSA public header includes switchdev.h, use the provided
switchdev_obj_dump_cb_t typedef for the object dump callback.

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