"IPv6 on by default" comment

[itojun@iijlab.net]

	due to my (lack of) English speaking skill i may not have delivered
	my comment to everyone, so i post it here again.

	with "there's no RA -> consider everything as onlink" portion of
	ND spec, there's ambiguity.  ND spec does not help us decide which
	interface we should use to send packet out.  i agree that ND spec needs
	clarification on this part (drop "everything as onlink" statement,
	clarify which outgoing interface should be used, etc).

	KAME implementation, by default, does not honor "consider everything as
	onlink" rule because of this ambiguity (therefore we won't experience
	the delay).
	if "default outgoing interface" gets configred to KAME kernel with
	ndp(8) command, the rule will be honored (and will experience the delay)

itojun