Fix NAN validate interface existence

Bug: 156879576
Test: atest android.hardware.wifi@1.0-service-tests

Change-Id: I8505e343f5b2ea5ea522cbb2ea344ff8914aea3d
diff --git a/wifi/1.4/default/wifi_iface_util.h b/wifi/1.4/default/wifi_iface_util.h
index f83d717..126b6ca 100644
--- a/wifi/1.4/default/wifi_iface_util.h
+++ b/wifi/1.4/default/wifi_iface_util.h
@@ -57,6 +57,7 @@
                                             IfaceEventHandlers handlers);
     virtual void unregisterIfaceEventHandlers(const std::string& iface_name);
     virtual bool setUpState(const std::string& iface_name, bool request_up);
+    virtual unsigned ifNameToIndex(const std::string& iface_name);
 
    private:
     std::array<uint8_t, 6> createRandomMacAddress();