ppp: Move ioctl definitions from if_ppp.h to new ppp-ioctl.h

This moves the definitions of the ioctls, constants and structures
relating to the ppp_generic interface to userspace out from if_ppp.h
to a new file, ppp-ioctl.h.  The new file has my copyright since I
designed and implemented the ppp_generic interface in the late 1990s.
None of the contents of this file comes from the original if_ppp.h
published by Carnegie Mellon University.

Of the remainder of if_ppp.h, only the PPP_MTU definition was being
used, and this replaces the uses of it with PPP_MRU (which is identical).
Therefore, this replaces the entire file with the single line

#include <linux/ppp-ioctl.h>

which clearly doesn't contain any CMU code.  Thus I have removed the
CMU copyright notice with its problematic advertising clause, and in
fact since it's only one trivial line I have not added any other
copyright notice.

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

Documentation/ioctl/ioctl-number.txt

@@ -255,7 +255,7 @@ Code  Seq#(hex)	Include File		Comments
 		linux/ixjuser.h		<http://web.archive.org/web/*/http://www.quicknet.net>
 'r'	00-1F	linux/msdos_fs.h and fs/fat/dir.c
 's'	all	linux/cdk.h
-'t'	00-7F	linux/if_ppp.h
+'t'	00-7F	linux/ppp-ioctl.h
 't'	80-8F	linux/isdn_ppp.h
 't'	90	linux/toshiba.h
 'u'	00-1F	linux/smb_fs.h		gone