Transceiver: Restrict conditions where FN gaps are detected

In pushRadioVector, like we did for driveTxPriorityQueue already, gaps
are possible in any channel for TRX!=0, since TRX0 is the only one
expected to be always transmitting.

Since we always need to transmit there, it makes no sense to check for
channel being not NONE.

Change-Id: I3b4b85b9100f69dfa113c54a4357120bd11ec86f

Transceiver52M/Transceiver.cpp

@@ -468,7 +468,7 @@ void Transceiver::pushRadioVector(GSM::Time &nowTime)
     } else {
       modFN = nowTime.FN() % state->fillerModulus[TN];
       bursts[i] = state->fillerTable[modFN][TN];
-      if (state->chanType[TN] != NONE) {
+      if (i == 0 && state->mFiller == FILLER_ZERO) {
         LOGCHAN(i, DTRXDDL, NOTICE) << "No Tx burst available for " << nowTime
                                     << ", retrans=" << state->mRetrans;
         state->ctrs.tx_unavailable_bursts++;