When a src/dst ip/port tuple is re-used before the pf state fully
expires we clean up the state and create a new one, unless syncookies
are enabled.
Test this, by running two back-to-back nc sessions, with a fixed source
port. Move the interface and IP to a different (vnet) jail, to trick the
network stack into letting us do this.
MFC after: 1 week
Event: Aberdeen hackathon 2022