net: switchdev: support static FDB addresses

This patch adds an ndm_state member to the switchdev_obj_fdb structure,
in order to support static FDB addresses.

Set Rocker ndm_state to NUD_REACHABLE.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Acked-by: Scott Feldman <sfeldma@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>