Start streaming of sound/SDR just before main loop

This prevents buffer overflow during init/creation processes

src/common/uhd.h

@@ -1,5 +1,6 @@
 
 int uhd_open(const char *device_args, double tx_frequency, double rx_frequency, double rate, double rx_gain, double tx_gain);
+int uhd_start(void);
 void uhd_close(void);
 int uhd_send(float *buff, int num);
 int uhd_receive(float *buff, int max);