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/frc971/autonomous/base_autonomous_actor.cc b/frc971/autonomous/base_autonomous_actor.cc
index df558ab..04ee334 100644
--- a/frc971/autonomous/base_autonomous_actor.cc
+++ b/frc971/autonomous/base_autonomous_actor.cc
@@ -29,7 +29,7 @@
   LOG(INFO, "resetting the drivetrain\n");
   max_drivetrain_voltage_ = 12.0;
   drivetrain_queue.goal.MakeWithBuilder()
-      .control_loop_driving(false)
+      .controller_type(0)
       .highgear(true)
       .wheel(0.0)
       .throttle(0.0)
@@ -58,7 +58,7 @@
   }
 
   auto drivetrain_message = drivetrain_queue.goal.MakeMessage();
-  drivetrain_message->control_loop_driving = true;
+  drivetrain_message->controller_type = 1;
   drivetrain_message->highgear = true;
   drivetrain_message->wheel = 0.0;
   drivetrain_message->throttle = 0.0;