net: mscc: ocelot: break out fdb operations into abstract implementations

To be able to implement a DSA front-end over ocelot_fdb_add,
ocelot_fdb_del, ocelot_fdb_dump, these need to have a simple function
prototype that is independent of struct net_device, netlink skb, etc.

So rename the ndo ops of the ocelot driver into
ocelot_port_fdb_{add,del,dump}, and have them all call the abstract
implementations. At the same time, refactor ocelot_port_fdb_do_dump into
a function whose prototype is compatible with dsa_fdb_dump_cb_t, so that
the do_dump implementations can live together and be called by the
ocelot_fdb_dump through a function pointer.

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