OsmoCtrl: use one global common counter for CTRL IDs

It is easier to traverse debugging logs if the CTRL request and response
IDs are globally unique across all programs and tests. Before this, we
were using 0 almost everywhere.

(This is not strictly needed for correctness, since each CTRL client has
its own request ID scope; just we open fairly many separate CTRL clients
all the time in our tests.)

Change-Id: I44c51f4fb5beb6cedf98ea0d6684a24c6aa418c7

src/osmo_gsm_tester/obj/osmo_ctrl.py

@@ -39,17 +39,17 @@ class CtrlInterfaceExn(Exception):
     pass
 
 class OsmoCtrl(log.Origin):
+    _next_id = 1
 
     def __init__(self, host, port):
         super().__init__(log.C_BUS, 'Ctrl', host=host, port=port)
         self.host = host
         self.port = port
         self.sck = None
-        self._next_id = 0
 
     def next_id(self):
-        ret = self._next_id
-        self._next_id += 1
+        ret = OsmoCtrl._next_id
+        OsmoCtrl._next_id += 1
         return ret
 
     def prefix_ipa_ctrl_header(self, data):