Unable to fully override netconf device capabilities

It's impossible to override device module-based capabilities with custom capabilities for custom modules. The default behavior in sal-netconf-connector is merge only and cannot be configured.

In some situations, it makes a lot of sense to completely override device yang models with app/user models. An example would be device with many models violating YANG RFC, but only a subset required in ODL. Then the easiest way is to fix broken models required by ODL, and set only those as device module-based capabilities.