feat(listen-func): add listen function for external call

Author: asas1asas200

src/rdm6300.cpp

@@ -117,3 +117,8 @@ uint32_t Rdm6300::get_tag_id(void)
 	_tag_id = 0;
 	return tag_id;
 }
+
+void Rdm6300::listen(void)
+{
+	_serial->listen();
+}

src/rdm6300.h

@@ -40,6 +40,7 @@ class Rdm6300
 		bool update(void);
 		uint32_t get_tag_id(void);
 		bool is_tag_near(void);
+		void listen(void);
 	private:
 #ifdef RDM6300_HARDWARE_SERIAL
 		HardwareSerial *_hardware_serial = NULL;