Make LinkProperties comparable.

Add equals() and hashcode() to LinkProperties and related fields.

Bug:3501569
Change-Id: Ifa737a67c16867ac43cf76bf618a483e612a189e
diff --git a/core/java/android/net/LinkAddress.java b/core/java/android/net/LinkAddress.java
index 9c36b12..f6a114c 100644
--- a/core/java/android/net/LinkAddress.java
+++ b/core/java/android/net/LinkAddress.java
@@ -78,6 +78,14 @@
             this.prefixLength == linkAddress.prefixLength;
     }
 
+    @Override
+    /*
+     * generate hashcode based on significant fields
+     */
+    public int hashCode() {
+        return ((null == address) ? 0 : address.hashCode()) + prefixLength;
+    }
+
     /**
      * Returns the InetAddress for this address.
      */