HAL_SITL: use a smaller buffer for real SITL UARTs

better emulation of real hw

libraries/AP_HAL_SITL/UARTDriver.cpp

@@ -307,6 +307,9 @@ void UARTDriver::_uart_start_connection(const char *path, uint32_t baudrate)
     if (!_connected) {
         ::printf("Opening %s\n", path);
         _fd = ::open(path, O_RDWR | O_CLOEXEC);
+        // use much smaller buffer sizes on real UARTs
+        _writebuffer.set_size(1024);
+        _readbuffer.set_size(512);
     }
 
     if (_fd == -1) {

libraries/AP_HAL_SITL/UARTDriver.h

@@ -83,18 +83,6 @@ private:
     static bool _select_check(int );
     static void _set_nonblocking(int );
 
-    /// default receive buffer size
-    static const uint16_t _default_rx_buffer_size = 128;
-
-    /// default transmit buffer size
-    static const uint16_t _default_tx_buffer_size = 16;
-
-    /// maxium tx/rx buffer size
-    /// @note if we could bring the max size down to 256, the mask and head/tail
-    ///       pointers in the buffer could become uint8_t.
-    ///
-    static const uint16_t _max_buffer_size = 512;
-
     SITL_State *_sitlState;
 
 };