394fa2b515
PR/203585 this appears to have been broken by r235959, which predates the ipfilter 5.1.2 import into FreeBSD. The IPv6 checksum calculation is incorrect. To resolve this we call in6_cksum() to do the the heavy lifting for us, through a new function ipf_pcksum6(). Should we need to revisit this area again, a DTrace probe is added to aid with future debugging. PR: 203275, 203585 MFC after: 1 month Differential Revision: https://reviews.freebsd.org/D20583