MFC r314651,r318439,r318440:

r314651:

sys/modules: normalize .CURDIR-relative paths to SRCTOP

This simplifies make output/logic

Tested with: `cd sys/modules; make ALL_MODULES=` on amd64

r318439:

Normalize .PATH on SRCTOP

This will help Jenkins dedupe 9 warnings between the static build and
the module build of ipsec(4).

Missed in SRCTOP conversion in r314651.

MFC with: r314651

r318440:

Normalize SYSDIR on SRCTOP instead of .CURDIR

This is being done to simplify pathing for CFLAGS and source files.

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

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

Clean up a bit of the INET/INET6 mess wrt options.

Use automated MK_INET*_SUPPORT code here as well.

After r274246 make the tree compile again.

gcc requires variables to be initialised in two places. One of them
is correctly used only under the same conditional though.

For module builds properly check if the kernel supports INET or INET6,
as otherwise various mips kernels without IPv6 support would fail to build.

Overhaul if_gre(4).

Split it into two modules: if_gre(4) for GRE encapsulation and
if_me(4) for minimal encapsulation within IP.

gre(4) changes:
* convert to if_transmit;
* rework locking: protect access to softc with rmlock,
protect from concurrent ioctls with sx lock;
* correct interface accounting for outgoing datagramms (count only payload size);
* implement generic support for using IPv6 as delivery header;
* make implementation conform to the RFC 2784 and partially to RFC 2890;
* add support for GRE checksums - calculate for outgoing datagramms and check
for inconming datagramms;
* add support for sending sequence number in GRE header;
* remove support of cached routes. This fixes problem, when gre(4) doesn't
work at system startup. But this also removes support for having tunnels with
the same addresses for inner and outer header.
* deprecate support for various GREXXX ioctls, that doesn't used in FreeBSD.
Use our standard ioctls for tunnels.

me(4):
* implementation conform to RFC 2004;
* use if_transmit;
* use the same locking model as gre(4);

PR: 164475
Differential Revision: D1023
No objections from: net@
Relnotes: yes
Sponsored by: Yandex LLC

Move most of the 15 variations on generating opt_inet.h and
opt_inet6.h into kmod.mk by forcing almost everybody to eat the same
dogfood. While at it, consolidate the opt_bpf.h and opt_mroute.h
targets here too.

Remove AppleTalk support.

AppleTalk was a network transport protocol for Apple Macintosh devices
in 80s and then 90s. Starting with Mac OS X in 2000 the AppleTalk was
a legacy protocol and primary networking protocol is TCP/IP. The last
Mac OS X release to support AppleTalk happened in 2009. The same year
routing equipment vendors (namely Cisco) end their support.

Thus, AppleTalk won't be supported in FreeBSD 11.0-RELEASE.

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.