Modbus polling rate is understood false

Modbus polling rate is taken for the subscription interval whereas it is the maximum polling rate in [the modbus binding](https://w3c.github.io/wot-binding-templates/bindings/protocols/modbus/ontology.html#haspollingtime). Even though this is a false understanding, I do not know how to fix it in the best possible way. Some thoughts:

1. The polling rate can be given as an interaction option. node-wot can check whether it is lower than the max rate. Is this clear from scripting api perspective?
2. The polling rate can be set in the config. Even though this would work, it would limit it to same number to all affordances and this may go against the binding template spec.