ppp: Change copyright notices from ANU to me

This changes the copyright notices on the PPP code that I developed
in the late 1990s from being copyright The Australian National
University to copyright Paul Mackerras.  I can do this as I have an
acknowledgement in writing from the Head of the Computer Science
Department at ANU (where I worked then) that ANU does not claim any
intellectual property in this code.

While I'm at it, change the copyright notice from BSD-style to
GNU GPL like the rest of the kernel.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: David S. Miller <davem@davemloft.net>