Reduce ADIS16470 rate to 1000 Hz

This reduces CPU usage on the roborio significantly, and since the
ADIS16470 is (ostensibly) averaging the 2000 Hz samples before we
process them, we shouldn't be losing too much information.

Change-Id: I5b94b3d00d5bcded119670674a49f47144c8d54d
diff --git a/frc971/wpilib/ADIS16470.cc b/frc971/wpilib/ADIS16470.cc
index fa61d9b..ec2ee9e 100644
--- a/frc971/wpilib/ADIS16470.cc
+++ b/frc971/wpilib/ADIS16470.cc
@@ -296,8 +296,9 @@
                   (0 << 2) /* internal clock mode */ |
                   (0 << 1) /* sync polarity, doesn't matter */ |
                   (1 << 0) /* data ready is active high */);
+          // Rate of the output will be 2000 / (DEC_RATE + 1) Hz.
           WriteRegister(registers::DEC_RATE,
-                        0 /* no internal decimation (averaging) */);
+                        1 /* Average every pair of values. */);
 
           // Start a sensor self test.
           WriteRegister(registers::GLOB_CMD, 1 << 2);