net: mscc: ocelot: unexport ocelot_port_fdb_do_dump from the common lib

ocelot_port_fdb_do_dump() is only used by ocelot_net.c, so move it
there.

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