termios ignores error codes delivered from low level drivers

[thomas.doerfler]

The low level UART driver functions listed in struct rtems_termios_callbacks are defined to return an integer value. For some of the calls (e.g. setAttributes), the exact value to be returned here is not yet defined and the return values are ignored (at least for firstOpen, lastClose and setAttributes).

It would be better if any non-zero return value from these calls would be interpreted as errors.

Actions required:

• identify the error coding scheme appropriate for this interface (rtems_status_code, errno coding, others...)

• identify possible changes to termios.c

• identify, which BSP might need reqork to avoid unintentional false error reportings

• implement changes

[Sebastian Huber]

Mark as fixed.