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.
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
src/sys/dev/an/if_an_pccard.c rev 1.10 change requires to include
"card_if.h" but Makefile doesn't know about this file. Without this,
kernel build will fail at this driver.
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.
