docs: add note from TrafficPolicy to PortTrafficPolicy as well

networking/v1alpha3/destination_rule.proto

@@ -219,6 +219,10 @@ message TrafficPolicy {
   ClientTLSSettings tls = 4;
 
   // Traffic policies that apply to specific ports of the service
+  // Note that port-level settings override the destination-level settings.
+  // Traffic settings specified at the destination-level will not be inherited
+  // when overridden by port-level settings, i.e. default values will be
+  // applied to fields omitted in port-level traffic policies.
   message PortTrafficPolicy {
     // Specifies the number of a port on the destination service
     // on which this policy is being applied.