It looks like I missed hooking in the pfsync printer in ee67461e. I think I messed up when redoing the sub-tree merge of `vendor/tcpdump` to `contrib/tcpdump` after 4bf98559. This is the only test I've done so far.
```
make -C /usr/src/usr.sbin/tcpdump clean
make -C /usr/src/usr.sbin/tcpdump
make -C /usr/src/usr.sbin/tcpdump install
```
`sudo /usr/sbin/tcpdump -i pfsync0`
After restarting pf, tcpdump shows
```
tcpdump: verbose output suppressed, use -v[v]... for full protocol decode
listening on pfsync0, link-type PFSYNC (Packet filter state syncing), snapshot length 262144 bytes
19:47:11.484907 19:47:11.484907 PFSYNCv5 len 48
clear all count 1
eof count 1^J
```
Any suggestions for further tests?