There was a patch[1] a few years ago, but apparently it didn't make it into mainline. At least looking in net/ipv4/tcp.c I haven't found any traces related to that.

However, I could have sworn that I've seen a similar patch in recent years, but either my memories are serving me wrong or I simply can't find it anymore.

Nevertheless, I didn't benchmark whether this is the case, nor was performance the main goal for writing ip2unix. So if performance is a concern, maybe benchmark with your specific workload?

https://www.spinics.net/lists/netdev/msg210741.html

Interesting. Thanks