Add working simple receiver test code

It makes all the motors spin back and forth, which is hilarious.

Change-Id: I150f07fbd91f71d725efa13d36f94dd2102b86d1
diff --git a/motors/medium_salsa.cc b/motors/medium_salsa.cc
index f2ee181..0b9d89d 100644
--- a/motors/medium_salsa.cc
+++ b/motors/medium_salsa.cc
@@ -243,7 +243,7 @@
   while (true) {
     unsigned char command_data[8];
     int command_length;
-    can_receive_command(command_data, &command_length, 0);
+    can_receive(command_data, &command_length, 0);
     if (command_length == 4) {
       uint32_t result = command_data[0] << 24 | command_data[1] << 16 |
                         command_data[2] << 8 | command_data[3];