Convert drivetrain mode from a bool to a number

This lets us support more than 2 drivetrain controller types in
perparation for splines.

Change-Id: I943d6073e6c5facae7223cc6111551a57b039a04
diff --git a/y2014/joystick_reader.cc b/y2014/joystick_reader.cc
index bc13be2..72c76ef 100644
--- a/y2014/joystick_reader.cc
+++ b/y2014/joystick_reader.cc
@@ -229,7 +229,7 @@
              .throttle(throttle)
              .highgear(is_high_gear_)
              .quickturn(data.IsPressed(kQuickTurn))
-             .control_loop_driving(is_control_loop_driving)
+             .controller_type(is_control_loop_driving ? 1 : 0)
              .left_goal(left_goal)
              .right_goal(right_goal)
              .left_velocity_goal(0)