Don't use AI_ADDRCONFIG when binding to wildcard addresses

Don't use AI_ADDRCONFIG when binding to wildcard addresses

https://bugzilla.redhat.com/show_bug.cgi?id=1098659

With parallel boot, network addresses might not yet be assigned [1],
but binding to wildcard addresses should work.

For non-wildcard addresses, ADDRCONFIG is still used. Document this
in libvirtd.conf.

[1] http://www.freedesktop.org/wiki/Software/systemd/NetworkTarget/