ipvs: Add simple weighted failover scheduler

Add simple weighted IPVS failover support to the Linux kernel. All
other scheduling modules implement some form of load balancing, while
this offers a simple failover solution. Connections are directed to
the appropriate server based solely on highest weight value and server
availability. Tested functionality with keepalived.

Signed-off-by: Kenny Mathis <kmathis@chokepoint.net>
Acked-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Simon Horman <horms@verge.net.au>