It is currently difficult to read the different steps involved in the
setup and teardown of ports in the DSA code. Keep it simple with a
single switch statement for each port type: UNUSED, CPU, DSA, or USER.

Also no need to call devlink_port_unregister from within dsa_port_setup
as this step is inconditionally handled by dsa_port_teardown on error.
Signed-off-by: Vivien Didelot <vivien.didelot@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>