net-next: dsa: move struct dsa_device_ops to the global header file

We need to access this struct from within the flow_dissector to fix
dissection for packets coming in on DSA devices.

Signed-off-by: Muciri Gatimu <muciri@openmesh.com>
Signed-off-by: Shashidhar Lakkavalli <shashidhar.lakkavalli@openmesh.com>
Signed-off-by: John Crispin <john@phrozen.org>
Signed-off-by: David S. Miller <davem@davemloft.net>