MFC r301549, r301550:
ng_mppc(4): Bring netgraph(3) MPPC compression support.

Support for compression has been available from July 2007 but it
was never imported due to concerns with patents once held by
STAC/HiFn. The issues have clearly been resolved so bring it
in now.

Special thanks to Brett Glass for preserving the code and
pointing documentation for the expiration case.

Taken from: mav (through Brett Glass)

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Don't use touch when what is really meant is :> (create an empty file, or
truncate it if it exists) or :>> (ensure the file exists, but don't change
it if it already does)

Reviewed by: ru
MFC after: 2 weeks

Let modules use the kernel's opt_*.h files if built along with
the kernel by wrapping all targets for fake opt_*.h files in
.if defined(KERNBUILDDIR). Thus, such fake files won't be
created at all if modules are built with the kernel.

Some modules undergo cleanup like removing unused or unneeded
options or .h files, without which they wouldn't build this way
or the other.

Reviewed by: ru
Tested by: no binary changes in modules built alone
Tested on: i386 sparc64 amd64

Take the rc4 code out of ng_mppc module so we don't fail to load when
we have the rc4 code already in the kernel (via wlan stuff or awi).
Add a dependency on the rc4 module so if it doesn't exist then load it.

Reviewed by: archie

Drop <bsd.man.mk> support from <bsd.kmod.mk>.

Not objected to by: -current

Use a consistent style and one much closer to the rest of /usr/src

When manual pages are moved or removed, MANX should be changed
to NOMAN.

Reported by: bde

Move the netgraph-related manual pages into share/man/man4/, as
discussed with archie.

Use .include <bsd.kmod.mk> to get to ../../*/conf/kmod.mk instead of
encoding the relative path.

AUTHOR -> AUTHORS

Move netgraph node type man pages from section 8 to section 4.

Pull in sys/conf/kmod.mk, rather than /usr/share/mk/bsd.kmod.mk.
This means that the kernel can be totally self contained now and is not
dependent on the last buildworld to update /usr/share/mk. This might
also make it easier to build 5.x kernels on 4.0 boxes etc, assuming
gensetdefs and config(8) are updated.

Zap KMODDEPS line

Revert to previous state, plus a few cleanups pointed out by bde.
Instead, make the decision as to whether to build this KLD in ../Makefile.

Turn off MPPE encryption if NOCRYPT is defined. If neither compression
nor encryption is enabled, don't build or install anything.

Add ng_mppc(8) netgraph node as a KLD module.

Obtained from: Whistle source tree