dsa: push cls_matchall setup_tc processing into a separate function

Let dsa_slave_setup_tc be a splitter for specific setup_tc types and
push out cls_matchall specific code into a separate function.

Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>