Supersedes ports/59442 and previous hasty-fix, and fixes the following:
- Build with __FreeBSD_version > 501114 (see bms commit)
- Build with new route.h (no RTF_PRCLONING)
- Don't use hardware assistance on framentation when DF is set.
- Allow pftcpdump -w to be used with pfsync.
Found-by: bento / Pyun YongHyeon
Submitted by: Max Laier