shrink the size of mavlink_message_t using max dialect message size

this makes mavlink_message_t much smaller, but setting
MAVLINK_MAX_PAYLOAD_LEN to the maximum message size in this
dialect. This saves us 320 bytes of memory

git-svn-id: https://arducopter.googlecode.com/svn/trunk@3239 f9c3cf11-9bcb-44bc-f272-b75c42450872

libraries/GCS_MAVLink/GCS_MAVLink.h

@@ -8,6 +8,11 @@
 
 #include <Stream.h>
 
+#include "include/ardupilotmega/version.h"
+
+// this allows us to make mavlink_message_t much smaller
+#define MAVLINK_MAX_PAYLOAD_LEN MAVLINK_MAX_DIALECT_PAYLOAD_SIZE
+
 #define MAVLINK_COMM_NUM_BUFFERS 2
 #include "include/mavlink_types.h"