tests: fix UDP multicast transport tests with IPv6

A valid scope id is always required on the multicast address

Change-Id: Ic676fcde0ee50daf75eb38c137e3cb917f43699f
diff --git a/daemon/face/multicast-udp-transport.hpp b/daemon/face/multicast-udp-transport.hpp
index 23c1e1d..5295238 100644
--- a/daemon/face/multicast-udp-transport.hpp
+++ b/daemon/face/multicast-udp-transport.hpp
@@ -62,16 +62,22 @@
   ssize_t
   getSendQueueLength() final;
 
+  /**
+   * \brief Opens and configures the receive-side socket
+   */
   static void
   openRxSocket(protocol::socket& sock,
                const protocol::endpoint& multicastGroup,
-               const boost::asio::ip::address& localAddress,
-               const shared_ptr<const ndn::net::NetworkInterface>& netif = nullptr);
+               const boost::asio::ip::address& localAddress = {},
+               const ndn::net::NetworkInterface* netif = nullptr);
 
+  /**
+   * \brief Opens and configures the transmit-side socket
+   */
   static void
   openTxSocket(protocol::socket& sock,
                const protocol::endpoint& localEndpoint,
-               const shared_ptr<const ndn::net::NetworkInterface>& netif = nullptr,
+               const ndn::net::NetworkInterface* netif = nullptr,
                bool enableLoopback = false);
 
 private: