net: add NetworkMonitorStub

refs #4024

Change-Id: I20da6f3351f51667b045987dc07e88ba814a4456
diff --git a/tests/unit-tests/net/network-monitor.t.cpp b/tests/unit-tests/net/network-monitor.t.cpp
index d23cb38..e46075b 100644
--- a/tests/unit-tests/net/network-monitor.t.cpp
+++ b/tests/unit-tests/net/network-monitor.t.cpp
@@ -53,7 +53,7 @@
   auto nm = make_unique<NetworkMonitor>(io);
   NM_REQUIRE_CAP(ENUM);
 
-  nm->onInterfaceAdded.connect([&] (const shared_ptr<NetworkInterface>&) {
+  nm->onInterfaceAdded.connect([&] (const shared_ptr<const NetworkInterface>&) {
     io.post([&] { nm.reset(); });
   });
   nm->onEnumerationCompleted.connect([&] {