Comment why we do a TLF when we get a ``Down'' event in state

Comment why we do a TLF when we get a ``Down'' event in state
``closing''.

Pointed out by: archie

Don't do a TLF when we get a ``Catastrphic Protocol Reject'' event
in state ``closed'' or ``stopped''.

Pointed out but not suggested by: archie

This makes no difference in the current implementation as
LcpLayerFinish() does nothing but log the event, but I disagree
in principle because it unbalances the TLF/TLS calls which
(IMHO) doesn't fit with the intentions of the RFC.

Maybe the RFC author had a reason for this.  It can only happen
in two circumstances:

- if LCP has already been negotiated then stopped or closed and we
  receive a protocol reject, then we must already have done a TLF.
  Why do one again and stay in the same state ?

- if LCP hasn't yet been started and we receive an unsolicted
  protocol reject, why should we TLF when we haven't done a TLS ?