Transceiver52M: HACK: Exit transceiver on POWEROFF command.

This hack allows OsmoBTS to correctly restart itself with different parameters.
We assume that transceiver is run as a service and will be restarted on exit.
diff --git a/Transceiver52M/Transceiver.cpp b/Transceiver52M/Transceiver.cpp
index 7bcbe14..ea5ca23 100644
--- a/Transceiver52M/Transceiver.cpp
+++ b/Transceiver52M/Transceiver.cpp
@@ -37,6 +37,8 @@
 #include "config.h"
 #endif
 
+extern volatile bool gbShutdown;
+
 using namespace GSM;
 
 #define USB_LATENCY_INTRVL		10,0
@@ -373,6 +375,10 @@
 
       mRadioInterface->stop();
       mDriveLoop->stop();
+
+      if (mPrimary) {
+        gbShutdown = true;
+      }
     }
   }
   else if (strcmp(command,"POWERON")==0) {