radioInterfaceMulti: Override setTxGain() to avoid chan!=0 calls

Change-Id: I7e67f660c3b0b009db59b405de603f6058021802
diff --git a/Transceiver52M/radioInterface.h b/Transceiver52M/radioInterface.h
index 945624a..83e00b9 100644
--- a/Transceiver52M/radioInterface.h
+++ b/Transceiver52M/radioInterface.h
@@ -134,6 +134,9 @@
   /** drive synchronization of Tx/Rx of USRP */
   void alignRadio();
 
+  /** set transmit gain */
+  virtual double setTxGain(double dB, size_t chan = 0);
+
   friend void *AlignRadioServiceLoopAdapter(RadioInterface*);
 };
 
@@ -157,6 +160,7 @@
 private:
   bool pushBuffer();
   int pullBuffer();
+  virtual double setTxGain(double dB, size_t chan);
 
   signalVector *outerSendBuffer;
   signalVector *outerRecvBuffer;