Add device-type, to ensure that plan --novpp generates MTU statements

vppcfg/config/__init__.py

@@ -77,7 +77,8 @@ class Validator:
 
     The purpose is to  ensure that the YAML file is both syntactically correct,
     which is ensured by Yamale, and semantically correct, which is ensured by a set
-    of built-in validators, and user-added validators (see the add_validator() method)."""
+    of built-in validators, and user-added validators (see the add_validator() method).
+    """
 
     def __init__(self, schema):
         self.logger = logging.getLogger("vppcfg.config")