On Linux, the serial connection was not setup properly, which led to
weird errors in the RFS server. This fix disables any input processing
in the termios layer, thus fixing the problem. Thanks to Markus Korber
for reporting and fixing the issue.
Read from the UART file descriptor until no data can be read
anymore (POSIX only). This is needed because sometimes the
RFS server didn't read all the available data and signaled errors.
