test: Add msgtype to msg_generic slots

Author: dergoegge

test/functional/test_framework/messages.py

@@ -1377,7 +1377,7 @@ def __repr__(self):
 # for cases where a user needs tighter control over what is sent over the wire
 # note that the user must supply the name of the msgtype, and the data
 class msg_generic:
-    __slots__ = ("data")
+    __slots__ = ("msgtype", "data")
 
     def __init__(self, msgtype, data=None):
         self.msgtype = msgtype