mlxsw: spectrum: remove FDB entry in case we get unknown object notification

It may happen that we get notification for FDB entry for object (port,
lag, vport), which does not exist. Currently we ignore that, which only
causes this being re-sent in next notification. The entry will never
disappear. So get rid of it by simply removing it using SFD register.

Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Reviewed-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>