Also see #12071.
Any non-specified interface gets a configuration like this:
I don't know if this is the best way. If you don't have DHCP servers
around, the startup will be like 10s slower. Anyway, user intervention
should probably be required when adding those extra interfaces. I'd
suggest putting ONBOOT=no for any NIC that hasn't been specified anywhere.
Should be fixed for next release (Brock, please be sure to test this)
Fix verified for beta2.