This branch uses tc to fixup the checksum. It's appearing to work with
the few guests I've tested so far, but there is an issue when a network
has <bandwidth> configured, and I don't want to post the patches for
review until I figure that out. In the meantime anyone who wants to test
with a non-<bandwidth> network, please do :-)
https://gitlab.com/lainestump/libvirt/-/tree/network-freebsd-checksum-fix...