DisjointPath should've been immutable.

Change-Id: I8499bd53acd62425c3aa8b0bce4958d6c0054712
diff --git a/core/api/src/main/java/org/onosproject/net/DisjointPath.java b/core/api/src/main/java/org/onosproject/net/DisjointPath.java
index 39237ea..8367067 100644
--- a/core/api/src/main/java/org/onosproject/net/DisjointPath.java
+++ b/core/api/src/main/java/org/onosproject/net/DisjointPath.java
@@ -30,7 +30,10 @@
      *
      * @return boolean corresponding to whether request to use
      *          backup was successful.
+     *
+     * @deprecated in 1.11.0
      */
+    @Deprecated
     boolean useBackup();
 
     /**