[SX127x] Added missing listen mode command (#72)

examples/SX127x/SX127x_Receive_Interrupt/SX127x_Receive_Interrupt.ino

@@ -76,6 +76,7 @@ void setup() {
   // lora.sleep()
   // lora.transmit();
   // lora.receive();
+  // lora.readData();
   // lora.scanChannel();
 }
 
@@ -153,6 +154,9 @@ void loop() {
 
     }
 
+    // put module back to listen mode
+    lora.startReceive();
+
     // we're ready to receive more packets,
     // enable interrupt service routine
     enableInterrupt = true;