Transceiver: Make error response to an unknown command on UDP command interface more understandable.

Previously we just repeated the last response which could confuse a command sender.

Signed-off-by: Tom Tsou <tom.tsou@ettus.com>
diff --git a/Transceiver52M/Transceiver.cpp b/Transceiver52M/Transceiver.cpp
index 75d61f3..5763772 100644
--- a/Transceiver52M/Transceiver.cpp
+++ b/Transceiver52M/Transceiver.cpp
@@ -838,6 +838,7 @@
   }
   else {
     LOG(WARNING) << "bogus command " << command << " on control interface.";
+    sprintf(response,"RSP ERR 1");
   }
 
   mCtrlSockets[chan]->write(response, strlen(response) + 1);