It is perfectly possible to have non zero indexed switches being present
in a DSA switch tree, in such a case, we will be deferencing a NULL
pointer while dsa_cpu_port_ethtool_{setup,restore}. Be more defensive
and ensure that dst->ds[0] is valid before doing anything with it.
Fixes: 0c73c523cf ("net: dsa: Initialize CPU port ethtool ops per tree")
Signed-off-by: Florian Fainelli <[email protected]>
Reviewed-by: Vivien Didelot <[email protected]>
Signed-off-by: David S. Miller <[email protected]>