Re: Bridge stays down until a port is added

And this might also allow to set an IPv6 address on a dummy interface, which Marc Haber reported as 
not being allowed for now, probably because DAD cannot succeed on a dummy interface and as such, a 
bind() cannot be allowed, and as such, setting the IPv6 address is currently useless.

For dummy, the interface should probably have the IFF_NOARP flag set.
There isn't any point in doing network discovery on a non-connected
interface. That would make DAD a no-op and bind would work.