STM32F7: serial: do not stop processing input in SW flow-control mode

arch/arm/src/stm32f7/stm32_serial.c

@@ -2224,6 +2224,22 @@ static bool up_rxflowcontrol(struct uart_dev_s *dev,
       /* Assert/de-assert nRTS set it high resume/stop sending */
 
       stm32_gpiowrite(priv->rts_gpio, upper);
+
+      if (upper)
+        {
+          /* With heavy Rx traffic, RXNE might be set and data pending.
+           * Returning 'true' in such case would cause RXNE left unhandled
+           * and causing interrupt storm. Sending end might be also be slow
+           * to react on nRTS, and returning 'true' here would prevent
+           * processing that data.
+           *
+           * Therefore, return 'false' so input data is still being processed
+           * until sending end reacts on nRTS signal and stops sending more.
+           */
+
+          return false;
+        }
+
       return upper;
     }