Tighten visibility of variable

Change-Id: Ia5cbed246414478d2f7de50ca6a67c4c6b2451b1
diff --git a/core/api/src/main/java/org/onosproject/net/flow/instructions/L0ModificationInstruction.java b/core/api/src/main/java/org/onosproject/net/flow/instructions/L0ModificationInstruction.java
index e0088c1..d8570c1 100644
--- a/core/api/src/main/java/org/onosproject/net/flow/instructions/L0ModificationInstruction.java
+++ b/core/api/src/main/java/org/onosproject/net/flow/instructions/L0ModificationInstruction.java
@@ -21,7 +21,7 @@
 
 public abstract class L0ModificationInstruction implements Instruction {
 
-    public static final String SEPARATOR = ":";
+    private static final String SEPARATOR = ":";
 
     /**
      * Represents the type of traffic treatment.