Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

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

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

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

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

Fix a bug whereby the physical endpoints of a gre(4) tunnel would not
be printed, if the module were loaded into a kernel which had INET6 enabled.

The gre(4) driver does not use INET6, nor is it specified for IPv6. The
tunnel_status() function in ifconfig(8) is somewhat overzealous and assumes
that all tunnel interfaces speak KAME ifioctls.

This fix follows the path of least resistance, by teaching gre(4) about
the two KAME ifioctls concerned.

PR: bin/56341

Finish driving a stake through the heart of netns and the associated
ifdefs scattered around the place - its dead Jim!

The SMB stuff had stolen AF_NS, make it official.

Since bpf is no longer an optional component, remove associated ifdef's.

Submitted by: don't quite remember - the name of the sender disappeared
with the rest of my inbox. :(

Cosmetics: #define NETATALK --> #define NETATALK 1, so that it is in line with
other #define FOO.

Add if_gre module glue.