net: mscc: ocelot: break apart ocelot_vlan_port_apply

This patch transforms the ocelot_vlan_port_apply function ("apply
what?") into 3 standalone functions:

- ocelot_port_vlan_filtering
- ocelot_port_set_native_vlan
- ocelot_port_set_pvid

These functions have a prototype that is better aligned to the DSA API.

The function also had some static initialization (TPID, drop frames with
multicast source MAC) which was not being changed from any place, so
that was just moved to ocelot_probe_port (one of the 6 callers of
ocelot_vlan_port_apply).

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