CLEAN UP SLIP INTERFACE TO KEEP FROM HANGING

CLEAN UP SLIP INTERFACE TO KEEP FROM HANGING

Here is a patch to clean up the interface between the tty-drivers, in
particular the com driver, and the sl# interfaces, this is not a work-around
but a genuine bug-fix.

Symptoms: after a number of "com#: silo overflow" SLIP ceases to work.

Overview of the problem:  the slip interface will disregard any notice
from the tty-driver on problems (parity errors, framing errors or overruns),
which basicly means the one might as well throw the packet away right away.
Also overrun in the packetizing will go relatively unnotized.

AUTHOR:         Poul-Henning Kamp (phk@data.fls.dk)
386BSD-Patchkit: patch00019