Add ::updateBaudRate(unsigned long baud) to change the baudrate after begin was called (#6494)

Author: Jeroen88

cores/esp8266/HardwareSerial.cpp

@@ -60,6 +60,15 @@ void HardwareSerial::end()
     _uart = NULL;
 }
 
+void HardwareSerial::updateBaudRate(unsigned long baud)
+{
+    if(!_uart) {
+        return;
+    }
+
+    uart_set_baudrate(_uart, baud);    
+}
+
 size_t HardwareSerial::setRxBufferSize(size_t size){
     if(_uart) {
         _rx_size = uart_resize_rx_buffer(_uart, size);
@@ -133,8 +142,8 @@ unsigned long HardwareSerial::detectBaudrate(time_t timeoutMillis)
     return detectedBaudrate;
 }
 
-size_t HardwareSerial::readBytes(char* buffer, size_t size)
-{
+size_t HardwareSerial::readBytes(char* buffer, size_t size)
+{
     size_t got = 0;
 
     while (got < size)
@@ -147,7 +156,7 @@ size_t HardwareSerial::readBytes(char* buffer, size_t size)
         got += read(buffer + got, std::min(size - got, avail));
     }
     return got;
-}
+}
 
 #if !defined(NO_GLOBAL_INSTANCES) && !defined(NO_GLOBAL_SERIAL)
 HardwareSerial Serial(UART0);

cores/esp8266/HardwareSerial.h

@@ -88,6 +88,8 @@ class HardwareSerial: public Stream
 
     void end();
 
+    void updateBaudRate(unsigned long baud);
+
     size_t setRxBufferSize(size_t size);
     size_t getRxBufferSize()
     {