Change the prototype of port_getnext to include a vid parameter.

This is necessary to introduce the support for VLAN.

Also rename the fdb_{add,del,getnext} function pointers to
port_fdb_{add,del,getnext} since they are specific to a given port.
Signed-off-by: NVivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>