rfc2217 handling also active when /dev/ttyXY is used

This results in data that looks like rfc2217 meta data not going to the user.

When connected via `microcom -p /dev/ttyXYZ' to an embedded board, the following happens:

    # echo -e '\xff\xfa\x2c\x6b\xb4\xff\xf0' 
    #

which is unexpected as it should generate some output. (Note the same when connected via telnet mode doesn't result in any output, which is a different bug though.)