This is xnu-8019. See this file in:
_in6_cksum:_inet6_cksum
_mbuf_data
_mbuf_inet6_cksum
_mbuf_len
_mbuf_next
_mbuf_nextpkt
_mbuf_pkthdr_header
_mbuf_pkthdr_len
_mbuf_pkthdr_rcvif
_mbuf_pkthdr_setheader
_mbuf_setlen
_mbuf_setnextpkt
_mbuf_type
_sysctl_register_fixed