Description of problem:
We store available features for particular controller in other_config of chassis
table. If we install a controller version that has new feature it gets added into other_config. However the flag is not cleared when user decides to downgrade below that feature. Northd still assumes that the controller supports the feature and generates logical flows accordingly, which might not work on the downgraded controller. 


Solution would be to keep list of known features and remove anything that is not part of that list.