gps: reopen the gps port on failed auto-detection

work-around for #9461

src/drivers/gps/gps.cpp

@@ -788,6 +788,17 @@ GPS::run()
 				case GPS_DRIVER_MODE_ASHTECH:
 					_mode = GPS_DRIVER_MODE_UBX;
 					usleep(500000); // tried all possible drivers. Wait a bit before next round
+
+					//FIXME: reopen the uart to work around an issue where the gps is not detected
+					// sometimes on startup on the mRo X2.1 board (see https://github.com/PX4/Firmware/issues/9461)
+					close(_serial_fd);
+					_serial_fd = ::open(_port, O_RDWR | O_NOCTTY);
+
+					if (_serial_fd < 0) {
+						PX4_ERR("failed to reopen the UART (%i)", errno);
+						request_stop();
+					}
+
 					break;
 
 				default: