Fix: add missing java docs for mapping management application

Change-Id: I712b21111fb23936213b7961244367583694c158
diff --git a/apps/mappingmanagement/api/src/main/java/org/onosproject/mapping/MappingEntry.java b/apps/mappingmanagement/api/src/main/java/org/onosproject/mapping/MappingEntry.java
index 6e6ef94..178f105 100644
--- a/apps/mappingmanagement/api/src/main/java/org/onosproject/mapping/MappingEntry.java
+++ b/apps/mappingmanagement/api/src/main/java/org/onosproject/mapping/MappingEntry.java
@@ -20,6 +20,9 @@
  */
 public interface MappingEntry extends Mapping {
 
+    /**
+     * Represents the type of mapping entry state.
+     */
     enum MappingEntryState {
 
         /**