Fix missing comma in method parameters

Change-Id: I21a34505eea96218f99aa90a2f78c9be5b7208ae
diff --git a/TestON/tests/USECASE/SegmentRouting/dependencies/up4.py b/TestON/tests/USECASE/SegmentRouting/dependencies/up4.py
index bfa9bb3..ad65697 100644
--- a/TestON/tests/USECASE/SegmentRouting/dependencies/up4.py
+++ b/TestON/tests/USECASE/SegmentRouting/dependencies/up4.py
@@ -396,7 +396,7 @@
             self.s1u_address, teid_up, sess_meter_idx)
 
     def downUeSessionOnosString(self, ue_address, down_id=None,
-                                tunn_peer_id=None, sess_meter_idx=DEFAULT_SESSION_METER_IDX
+                                tunn_peer_id=None, sess_meter_idx=DEFAULT_SESSION_METER_IDX,
                                 **kwargs):
         if down_id is not None:
             tunn_peer_id = down_id