MFC 230453, 230726, 252015, 252426:

- ipv6_enable + ipv6_gateway_enable should unset ACCEPT_RTADV by default for
  backward compatibility.

- Configurations in ipv6_prefix_IF should be recognized even if there is no
  ifconfig_IF_ipv6.

- DAD wait should be performed at once, not on a per-interface basis, if
  possible.  This fixes an issue that a system with a lot of IPv6-capable
  interfaces takes too long for booting.

- Add CIDR notation support like 192.168.1-2.10-16/24 to $ifconfig_IF_aliasN.
  This is an extended version of ipv4_addr_IF which supports both IPv4 and
  IPv6, and multiple range specifications.  To avoid to generate too many
  addresses, the maximum number of the generated addresses is currently
  limited to 31.

- Add $ifconfig_IF_aliases, which accepts multiple IP aliases in a variable.

- ipv6_prefix_IF now supports !/64 prefix length.  In addition to the old
  64-bit format (2001:db8:1:1), a full 128-bit format like 2001:db8:1:1::/64
  is supported.

- Replace ifconfig command with $IFCONFIG_CMD variable to support
  a dry-run mode in the future.

- Remove IP aliases before removing all of IPv4 addresses when doing
  "rc.d/netif down".

- Add a DAD wait to network6_getladdr() because it is possible to fail to
  configure an EUI64 address when ipv6_prefix_IF is specified.
MFC 243441:

Support a flag for ALLOW/BLOCK in source-specific multicast (RFC 4604).
MFC 243324:

Do not put "already running" message when rc_quiet=yes.

PR:	bin/165477
MFC 242301:

Load ipdivert.ko when natd_enable=YES.

PR:	conf/167566
MFC 242184:

Add setfib(1) support for services as <name>_fib in rc.conf.
MFC 243185, 243188, 243212:

Add -fib modifier to specify FIB number.  The FIB number can be in a
comma-separated list and/or range specification:

 # route add -inet 192.0.2.0/24 198.51.100.1 -fib 1,3-5,6

Although all of the subcommands supports the modifier, "monitor" does not
support the list or range specification at this moment.