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

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.

Use src.opts.mk in preference to bsd.own.mk except where we need stuff
from the latter.

bridgestp is now a seperate module.

Allow bridge and carp to play nicely together by returning the packet if its
destined for a carp interface.

Obtained from: OpenBSD
MFC after: 2 weeks

Reimplementation of world/kernel build options. For details, see:

http://lists.freebsd.org/pipermail/freebsd-current/2006-March/061725.html

The src.conf(5) manpage is to follow in a few days.

Brought to you by: imp, jhb, kris, phk, ru (all bugs are mine)

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 deprecated name, and let kmod.mk create an empty .h file.

Connect if_bridge to the build.

Approved by: mlaier (mentor)