net: dsa: felix: directly call ocelot_port_{set,unset}_dsa_8021q_cpu

Absorb the final details of calling ocelot_port_{,un}set_dsa_8021q_cpu(),
i.e. the need to lock &ocelot->fwd_domain_lock, into the callee, to
simplify the caller and permit easier code reuse later.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>