This is a combination of two patches from [[ https://github.com/freebsd/freebsd/compare/master...intel-wired-ethernet:ixl-iflib | ixl-iflib ]] in the intel-wired-ethernet GitHub repository.
[[ https://github.com/freebsd/freebsd/commit/3da3c7ccaaf07ba9b4bd2cc6f0b850f45ecb8581 | 3da3c7ccaaf0 ]] iflib: Save TCP header length during packet parsing when CSUM_IP6_TCP is set
[[ https://github.com/freebsd/freebsd/commit/9adced371d84df418dfc40f9189bf084f509054b | 9adced371d84 ]] iflib: Save TCP header length when TCP checksum offload is requested.