Disable DAD for downstream interfaces when tethering

Bug: 30298058
Change-Id: If4cd1f2e2b782ff08d667eb065138c06559b3394
diff --git a/server/InterfaceController.cpp b/server/InterfaceController.cpp
index 4129c0f..eac4fbf 100644
--- a/server/InterfaceController.cpp
+++ b/server/InterfaceController.cpp
@@ -136,6 +136,14 @@
     return writeValueToPath(ipv6_proc_path, interface, "accept_dad", accept_dad);
 }
 
+int InterfaceController::setIPv6DadTransmits(const char *interface, const char *value) {
+    if (!isIfaceName(interface)) {
+        errno = ENOENT;
+        return -1;
+    }
+    return writeValueToPath(ipv6_proc_path, interface, "dad_transmits", value);
+}
+
 int InterfaceController::setIPv6PrivacyExtensions(const char *interface, const int on) {
     if (!isIfaceName(interface)) {
         errno = ENOENT;