Fix toString in UPF UE Sessions and Terminations

Change-Id: I90c9d3180ba9cbbd688ccadd5734792c13504c56
diff --git a/core/api/src/main/java/org/onosproject/net/behaviour/upf/SessionUplink.java b/core/api/src/main/java/org/onosproject/net/behaviour/upf/SessionUplink.java
index 70db84c..a2f0460 100644
--- a/core/api/src/main/java/org/onosproject/net/behaviour/upf/SessionUplink.java
+++ b/core/api/src/main/java/org/onosproject/net/behaviour/upf/SessionUplink.java
@@ -72,7 +72,7 @@
 
     @Override
     public String toString() {
-        return "UESessionUL{" + matchString() + " -> " + actionString();
+        return "UESessionUL{" + matchString() + " -> " + actionString() + "}";
     }
 
     private String matchString() {