P4 Language Specification Document (https://p4.org/p4-spec/docs/P4-16-working-spec.html#sec-control) specifies that control declarations (along with parser declarations) cannot have generic values in them. ControlTypeDeclaration can have generic types in them but not ControlDeclaration. But p4c allows that happen as in the case of generic.p4i
Need to check what is valid