How to configure specific router address to advertise with rtadvd?

[Darren Pilgrim]

I have a machine I want to do IPv6 routing.  The interface out which its 
sending router advertisements has multiple static IPv6 addresses 
assigned from the same prefix.  The problem is rtadvd is selecting the 
"wrong" address for the router.  The man page for rtadvd.conf doesn't 
indicate how to do this.  How do I tell rtadvd which address to 
advertise as the router?