Minor improvements.

Update values from RFC 8319

branches: 1.18.28;
Add support for the noifprefix keyword which stops rtadvd(8) gathing prefix
information from the interface if no addrs are present in rtadvd.conf(5).

branches: 1.17.2;
Add capfile(5) to describe the termcap format.
Adjust various man pages and other documentation to point to capfile(5)
instead of termcap(5).
Remove getcap(3) as curses hasn't been building it for a long time.
Punt wrterm.c as tset no longer uses it.

- improve wording;
- replace references to resolver(5) with ones to resolv.conf(5);
- remove references to FreeBSD (which were copied 1:1 from their
man page).

From patch by Bug Hunting.

Add RDNSS and DNSSL support, RFC6106.
Replace custom lists with TAILQ lists.
Clean up plently of signed vs unsigned warnings and set WARNS=4.

Adapted from FreeBSD.

branches: 1.14.6;
Use documentation prefix.
Drop trailing whitespace.
Remove repeated word.
Bump date.

Kill -offset without argument.

branches: 1.12.16;
NDP-related improvements:
RFC4191
- supports host-side router-preference

RFC3542
- if DAD fails on a interface, disables IPv6 operation on the
interface
- don't advertise MLD report before DAD finishes

Others
- fixes integer overflow for valid and preferred lifetimes
- improves timer granularity for MLD, using callout-timer.
- reflects rtadvd's IPv6 host variable information into kernel
(router only)
- adds a sysctl option to enable/disable pMTUd for multicast
packets
- performs NUD on PPP/GRE interface by default
- Redirect works regardless of ip6_accept_rtadv
- removes RFC1885-related code

From the KAME project via SUZUKI Shinsuke.
Reviewed by core.

Bump date for recent changes.

need "a". from jmc@openbsd

sync manpage with previous change (addrs# deprecdated)

between with three es, and positive with two is.

Drop a .Pp.

make it clearer that /etc/rtadvd.conf is optional (normally,
configurations were derived from kernel interface settings).

install rtadvd.conf into /usr/share/exapmles/rtadvd, instead of /etc.

sync with kame.

sync with latest kame tree.
- reduce chances for signal handler rae condition
- decrease chances for misconfiguration
- feedbacks from router renumbering protocol bakeoff

sync with sys/netinet/icmp6.h change (no bitfield for router renumber).
more logging. improve error handling/garbage collection. sync with kame.

branches: 1.3.4;
sync with latest kame.
- decrease warning level on missing rtadvd.conf (actually, the file
can be omitted)
- strict prototype
- gather stats better, emit stats on SIGUSR1 to /var/run

fix typo (no comma).
use NetBSD RCS ID, retain original.

rtadvd: advertise IPv6 prefix info via router advertisement.
(to be run on routers)