AP_GPS: force flow control off on GPS serial ports

libraries/AP_GPS/AP_GPS.cpp

@@ -183,6 +183,7 @@ AP_GPS::detect_instance(uint8_t instance)
 		}
 		uint32_t baudrate = pgm_read_dword(&_baudrates[dstate->last_baud]);
 		_port[instance]->begin(baudrate);
+		_port[instance]->set_flow_control(AP_HAL::UARTDriver::FLOW_CONTROL_DISABLE);
 		dstate->last_baud_change_ms = now;
         send_blob_start(instance, _initialisation_blob, sizeof(_initialisation_blob));
     }