Fix IPAddress Type mismatch between echo-requester and echo-responder.

When using TCP, the echo-server was listening over IPv4 while the
echo-requester was getting configured for IPv6.

Normalize both sides to always use IPv6 over both TCP or MRP.

src/messaging/tests/echo/echo_responder.cpp

@@ -84,11 +84,7 @@ int main(int argc, char * argv[])
     if (useTCP)
     {
         err = gTCPManager.Init(chip::Transport::TcpListenParameters(chip::DeviceLayer::TCPEndPointManager())
-#if INET_CONFIG_ENABLE_IPV4
-                                   .SetAddressType(chip::Inet::IPAddressType::kIPv4)
-#else
                                    .SetAddressType(chip::Inet::IPAddressType::kIPv6)
-#endif
         );
         SuccessOrExit(err);