Multipath routing - failover version

[Li, Qing]

	Hi,

	I recently incorporated multipath support into -CURRENT,
	for the upcoming 8.0.  This patch originated from the KAME
	project and builds on the existing routing data structures
	and infrastructure. As a result I did not have to
	modify the userland programs, however, I think netstat
	can use some tweaking in its output. 

	I am in the process of incorporating additional functionalities
	such as allowing for preference setting, and performing active 
	health-check on the gateways and updating the routes
accordingly.

> 
> Switching between different paths is done by the kernel based 
> on the link state of the interface associated with the 
> gateway. This way when can achieve a level of redundancy at 
> the link level (this is not a routing protocol!).
> 

	Hmm... in the current code if_unroute() would remove
	the interface route when the interface is down.


	-- Qing