mlx5e: push cls_flower and mqprio setup_tc processing into separate functions

Let mlx5e_setup_tc (former mlx5e_ndo_setup_tc) be a splitter for specific
setup_tc types and push out cls_flower and mqprio specific codes into
separate functions. Also change the return values so they are the same
as in the rest of the drivers.

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