- to eliminate extra overhead in loopback interface code
	- to avoid data copies during IPv6/IPsec processing
	I'll add "options PULLDOWN_TEST" for all the platforms.  the option
	will make use of m_pulldown function during IPv4/v6 header processing.

	I have made fair amount of tests for IPv4 and IPv6, however, not yet
	sure if there's any assumption in other code that conflicts with
	m_pulldown framework.
	for example: data placement in mbuf chain will be different for IPv4/v6,
	so i'd expect some change in appletalk-over-IPv4 or, more importantly,
	appletalk-over-IPv4-with-IPsec.  in most cases it should work fine
	(if appletalk processing calls enough m_pullup), but sometimes code
	makes assumption on inbound mbuf data placement.

	please report if you have any problems.  I plan to put it for certain
	amount of time in main trunc only, and merge it eventually into 1.5
	branch.

itojun