Remark from projectkk2glider taken into account

Serial2 connection and USB CDC output now waits there is some free space
before adding anything to the buffer

radio/src/debug.cpp

@@ -61,7 +61,6 @@ void debugPrintf(const char * format, ...)
 #if defined(DEBUG_TRACE_BUFFER)
 static struct TraceElement traceBuffer[TRACE_BUFFER_LEN];
 static uint8_t traceBufferPos;
-extern Fifo<512> uart3TxFifo;
 gtime_t filltm(gtime_t *t, struct gtm *tp);
 
 void trace_event(enum TraceEvent event, uint32_t data)
@@ -107,7 +106,7 @@ void dumpTraceBuffer()
     TRACE("  %03d    0x%08x", traceBuffer[n].event, traceBuffer[n].data);  
     if (traceBuffer[n].time == 0 && traceBuffer[n].time_ms == 0) break;
     if ((n % 5) == 0) {
-      while (!uart3TxFifo.empty()) { 
+      while (!serial2TxFifo.empty()) { 
         CoTickDelay(1);
       }
     }