[NRRPLT-7553] Add legacyMode tag to diff drive plugin

Merged in NRRPLT-7553-clean-up-pioneer-robot-red-errors (pull request #52)

Approved-by: Eloy Retamino
Approved-by: Manos Angelidis

p3dx/pioneer3dx.sdf

@@ -411,6 +411,7 @@
     </plugin>
     <plugin name='differential_drive_controller' filename='libgazebo_ros_diff_drive.so'>
       <alwaysOn>true</alwaysOn>
+      <legacyMode>true</legacyMode>
       <updateRate>100</updateRate>
       <leftJoint>base_right_wheel_joint</leftJoint>
       <rightJoint>base_left_wheel_joint</rightJoint>