[CentOS] Centos 7 as gateway - UDP performance is busted/awful?

I think I have my answer: The kernel is busted (or something
isn't loaded that I need, but don't know about :-).

I copied my Fedora 20 desktop 3.15.8-200.fc20.x86_64 kernel
and /lib/module files to the centos7 KVM host, rebuilt
grub.cfg, and rebooted into the 3.15.8-200 kernel, and
with no other changes the UDP packet forwarding is now working
perfectly.

I guess it is time to make yet another bugzilla account
and submit a bug...