AP_SerialManager: disable flow control for sbus1 port

libraries/AP_SerialManager/AP_SerialManager.cpp

@@ -240,6 +240,7 @@ void AP_SerialManager::init()
                     state[i].uart->configure_parity(2);    // enable even parity
                     state[i].uart->set_stop_bits(2);
                     state[i].uart->set_unbuffered_writes(true);
+                    state[i].uart->set_flow_control(AP_HAL::UARTDriver::FLOW_CONTROL_DISABLE);
                     break;
             }
         }