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

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

- Implement RDNSS and DNSSL options (RFC 6106, IPv6 Router Advertisement
Options for DNS Configuration) into rtadvd(8) and rtsold(8). DNS
information received by rtsold(8) will go to resolv.conf(5) by
resolvconf(8) script. This is based on work by J.R. Oldroyd (kern/156259)
but revised extensively[1].

- rtadvd(8) now supports "noifprefix" to disable gathering on-link prefixes
from interfaces when no "addr" is specified[2]. An entry in rtadvd.conf
with "noifprefix" + no "addr" generates an RA message with no prefix
information option.

- rtadvd(8) now supports RTM_IFANNOUNCE message to fix crashes when an
interface is added or removed.

- Correct bogus ND_OPT_ROUTE_INFO value to one in RFC 4191.

Reviewed by: bz[1]
PR: kern/156259 [1]
PR: bin/152458 [2]

- supported a string notation for xxflags.
- deprecate routes#N, as it is hard to keep consistency with
rtprefixN. accept any number of "rtprefix", "rtrefix0",
..., "rtprefix99".
- deprecate "addrs#N", as it is difficult for users to keep
consistency with "addrN".
accept 100 prefix info in maximum - like "addr", "addr0"
... "addr99". WARNS=2 clean on netbsd.
old configuration file should work just fine.
behavior change:
previously, we rejected "addrN" if there's "addr", and we rejected
"addr" if there is "addrN". now we accept both without problem.
- when an advertised prefix configured from the kernel has been added
or invalidated, notice the change in a short delay.
- when invalidating a prefix, do not bark even if there is
inconsistency about prefix lifetimes.
- wrap more specific route info code into ROUTEINFO.

Obtained from: KAME
MFC after: 1 week

make it clearer that rtadvd.conf is optional (configs are grabbed from kernel).

Sync with latest KAME

Obtained from: KAME

libipsec and IPsec related apps. (and some KAME related man pages)

Reviewed by: freebsd-arch, cvs-committers
Obtained from: KAME project