Fix Javadoc warnings

Change-Id: Icf8b6b6f77ea80d3975aa975226a178145067adf
diff --git a/core/api/src/main/java/org/onosproject/net/link/ProbedLinkProvider.java b/core/api/src/main/java/org/onosproject/net/link/ProbedLinkProvider.java
index 6a04f83..3b633ac 100644
--- a/core/api/src/main/java/org/onosproject/net/link/ProbedLinkProvider.java
+++ b/core/api/src/main/java/org/onosproject/net/link/ProbedLinkProvider.java
@@ -36,6 +36,9 @@
     /**
      * Build a stringified MAC address using the ClusterMetadata hash for uniqueness.
      * Form of MAC is "02:eb" followed by four bytes of clusterMetadata hash.
+     *
+     * @param cm cluster metadata
+     * @return stringified mac address
      */
     static String fingerprintMac(ClusterMetadata cm) {
         if (cm == null) {