The mv88e6xxx driver currently assumes a single CPU port in the fabric
and thus floods frames with unknown DA on a single DSA port, the one
that is one hop closer to the CPU port.

With multiple CPU ports in mind, this isn't true anymore because CPU
ports could be found behind both DSA ports of a device in-between
others.

For example in a A <-> B <-> C fabric, both A and C having CPU ports,
device B will have to flood such frame to its two DSA ports.

This patch considers both CPU and DSA ports of a device as upstream
ports, where to flood frames with unknown DA addresses.
Signed-off-by: NVivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>