Making base frame ID for map to base link transform based on base fra…

…me ID parameter (#4632)

Signed-off-by: Steve Macenski <stevenmacenski@gmail.com>

nav2_loopback_sim/nav2_loopback_sim/loopback_simulator.py

@@ -166,7 +166,7 @@ def initialPoseCallback(self, msg):
         # Adjust map->odom transform based on new initial pose, keeping odom->base_link the same
         t_map_to_base_link = TransformStamped()
         t_map_to_base_link.header = msg.header
-        t_map_to_base_link.child_frame_id = 'base_link'
+        t_map_to_base_link.child_frame_id = self.base_frame_id
         t_map_to_base_link.transform.translation.x = self.initial_pose.position.x
         t_map_to_base_link.transform.translation.y = self.initial_pose.position.y
         t_map_to_base_link.transform.translation.z = 0.0