Initialize mDefaultNetId.

This was accidentally dropped in the merge from master-multinetwork-dev to
master, in http://ag/465644.

Change-Id: I0699604923477e6b19dfc8c70a84c50a79fe3d72
diff --git a/NetworkController.cpp b/NetworkController.cpp
index 3cf82bd..a11fae8 100644
--- a/NetworkController.cpp
+++ b/NetworkController.cpp
@@ -38,7 +38,8 @@
 
 NetworkController::NetworkController(PermissionsController* permissionsController,
                                      RouteController* routeController)
-        : mPermissionsController(permissionsController),
+        : mDefaultNetId(NETID_UNSET),
+          mPermissionsController(permissionsController),
           mRouteController(routeController) {
 }