mobility: Allow AssignStreams after construction for SteadyStateRwpMo…

…bility

The SteadyStateRandomWaypointMobilityModel should support AssignStreams()
after object construction, but prior to this patch, it would cause a
segmentation fault until after initialization.  The initial benefit is
the prevention of test suite failures due to random stream assignment.

src/mobility/model/steady-state-random-waypoint-mobility-model.cc

@@ -95,6 +95,7 @@ SteadyStateRandomWaypointMobilityModel::SteadyStateRandomWaypointMobilityModel (
   m_u_r = CreateObject<UniformRandomVariable> ();
   m_x = CreateObject<UniformRandomVariable> ();
   m_y = CreateObject<UniformRandomVariable> ();
+  m_position = CreateObject<RandomBoxPositionAllocator> ();
 }
 
 void
@@ -115,7 +116,6 @@ SteadyStateRandomWaypointMobilityModel::DoInitializePrivate (void)
   m_speed->SetAttribute ("Max", DoubleValue (m_maxSpeed));
   NS_ASSERT (m_minX < m_maxX);
   NS_ASSERT (m_minY < m_maxY);
-  m_position = CreateObject<RandomBoxPositionAllocator> ();
   m_x->SetAttribute ("Min", DoubleValue (m_minX));
   m_x->SetAttribute ("Max", DoubleValue (m_maxX));
   m_y->SetAttribute ("Min", DoubleValue (m_minY));

src/mobility/test/steady-state-random-waypoint-mobility-model-test.cc

@@ -82,7 +82,7 @@ SteadyStateRandomWaypointTest::DoRun (void)
     {
       // Create a new mobility model.
       Ptr<MobilityModel> model = mobilityFactory.Create ()->GetObject<MobilityModel> ();
-
+      model->AssignStreams (100 * (i + 1));
       // Add this mobility model to the stack.
       mobilityStack.push_back (model);
       Simulator::Schedule (Seconds (0.0), &Object::Initialize, model);