A couple of pepole noted that SLIP would blow chunks periodically with
newer kernels.  This is because I forgot to add back some code to make
splimp() > spltty() in the presence of SLIP and PPP, and without this
some structures are not locked correctly.

Anyway, I just fixed this.  Version 1.21 of intr.c should make said
users happy.  (Note that you don't need the reset of this week's
changes to use it, for people who are afraid...)


------------------------------------------------------------------------------