net: dsa: Fix legacy probing

net: dsa: Fix legacy probing

After commit 3c88e43c9ad9 ("net: dsa: Remove master_netdev and
use dst->cpu_dp->netdev") and a6d2804a874d ("net: dsa: Associate
slave network device with CPU port") we would be seeing NULL pointer
dereferences when accessing dst->cpu_dp->netdev too early. In the legacy
code, we actually know early in advance the master network device, so
pass it down to the relevant functions.

Fixes: 3c88e43c9ad9 ("net: dsa: Remove master_netdev and use dst->cpu_dp->netdev")
Fixes: a6d2804a874d ("net: dsa: Associate slave network device with CPU port")
Reported-by: Jason Cobham <jcobham@questertangent.com>
Tested-by: Jason Cobham <jcobham@questertangent.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>