trivial multicast support, and support for xon/xoff output flow
control to the PPP subsystem. Fixed several bugs, including making
the accumulation and resetting of statistics more consistent. State
for the VJ compressor is now dynamically allocated.
improvements. The PPP kernel code is now split into if_ppp.c,
containing generic PPP support, and ppp_tty.c, which specifically
supports PPP on async tty devices (as a line discipline). This is
so that other devices can be supported without making them look
like ttys.
