add flush functions for serial helpers

src/fsfw_hal/linux/serial/helper.cpp

@@ -161,3 +161,7 @@ void uart::setStopbits(struct termios& options, StopBits bits) {
     options.c_cflag &= ~CSTOPB;
   }
 }
+
+void uart::flushRxBuf(int fd) { tcflush(fd, TCIFLUSH); }
+
+void uart::flushTxRxBuf(int fd) { tcflush(fd, TCIOFLUSH); }

src/fsfw_hal/linux/serial/helper.h

@@ -64,6 +64,9 @@ void setParity(struct termios& options, Parity parity);
 
 void ignoreCtrlLines(struct termios& options);
 
+void flushRxBuf(int fd);
+void flushTxRxBuf(int fd);
+
 int readCountersAndErrors(int serialPort, serial_icounter_struct& icounter);
 
 }  // namespace uart