MFC r350064:

As of upstream fil.c CVS r1.53 (March 1, 2009), prior to the import of
ipfilter 5.1.2 into FreeBSD-10, the fix for, 2580062 from/to targets
should be able to use any interface name, moved frentry.fr_cksum to
prior to frentry.fr_func thereby making this code redundant. After
investigating whether this fix to move fr_cksum was correct and if it
broke anything, it has been determined that the fix is correct and this
code is redundant. We remove it here.