OpenBSD network stack evolution

Dealing with the IP checksum and the protocol checksums (foremost TCP and UDP) in the network stack is surprisingly complex. Having stumbled over an unexpected performance penalty from the IP checksum, I always had this area on my mental todo - and when we stumbled over a really nasty piece of code in pf dealing with these checksums, I re-evaluated and changed the IP checksumming in our stack, for performance and to make better use of checksum offloading to network cards. Changing the protocol checksums in the same way is harder and in the works.