Some USB modems (reportedly, USRobotics USB modem) don't strip the parity bit
of data received from modem connections operating in < 8 bit modes
(e.g. 7-E-1), as is normally don't with a modem connected to a UART, so we'll
do that stripping (forcing to 0) here, as recommended by Deuce.

Nelgin, if you're doing some manually stripping of the 7th bit bytes received
from 7-E-1 connected modems and then sent to your server/BBS over TCP, you
shouldn't need to do that now.