randomize time sync seq nr

include/timesync.h

@@ -9,6 +9,7 @@
 //#define TIME_SYNC_TRIGGER 100 // threshold for time sync [milliseconds]
 #define TIME_SYNC_FRAME_LENGTH 0x07 // timeserver answer frame length [bytes]
 #define TIME_SYNC_FIXUP 4 // calibration to fixup processing time [milliseconds]
+#define TIMEREQUEST_MAX_SEQNO 0xf0 // threshold for wrap around seqno
 
 void timesync_init(void);
 void send_timesync_req(void);