[test] Add P2P_SERVICES to p2p.py

The messages.py module should contain code and helpers for
[de]serializing p2p messages. Specific usage of those messages should
be in p2p.py. Therefore specify the nServices value in the calling code,
not in the messages.py module.

test/functional/test_framework/messages.py

@@ -1022,7 +1022,7 @@ class msg_version:
 
     def __init__(self):
         self.nVersion = 0
-        self.nServices = NODE_NETWORK | NODE_WITNESS
+        self.nServices = 0
         self.nTime = int(time.time())
         self.addrTo = CAddress()
         self.addrFrom = CAddress()