Make message bridge issues with localizer clearer

Rather than just indicating image too old/from future, actually indicate
if the message bridge appears to be disconnected.

Change-Id: I10b469349e4fc0149d3844c2fb3f9b98f6ed2545
Signed-off-by: James Kuszmaul <jabukuszmaul@gmail.com>
diff --git a/y2020/control_loops/drivetrain/localizer_debug.fbs b/y2020/control_loops/drivetrain/localizer_debug.fbs
index e94d251..794cf13 100644
--- a/y2020/control_loops/drivetrain/localizer_debug.fbs
+++ b/y2020/control_loops/drivetrain/localizer_debug.fbs
@@ -10,6 +10,7 @@
   IMAGE_TOO_OLD = 6,
   NONFINITE_MEASUREMENT = 7,
   CORRECTION_TOO_LARGE = 8,
+  MESSAGE_BRIDGE_DISCONNECTED = 9,
 }
 
 table ImageMatchDebug {