Add implementation of getInterfaceHash()

Bug: 136065010
Test: m
Change-Id: I314f19aeca82cc8653eab71c9526ea7a208e6b50
diff --git a/Tethering/src/android/net/dhcp/DhcpServerCallbacks.java b/Tethering/src/android/net/dhcp/DhcpServerCallbacks.java
index 7c41377..9fda125 100644
--- a/Tethering/src/android/net/dhcp/DhcpServerCallbacks.java
+++ b/Tethering/src/android/net/dhcp/DhcpServerCallbacks.java
@@ -28,4 +28,9 @@
     public int getInterfaceVersion() {
         return IDhcpServerCallbacks.VERSION;
     }
+
+    @Override
+    public String getInterfaceHash() {
+        return IDhcpServerCallbacks.HASH;
+    }
 }