While testing at NF we have found this incorrect KASSERT. It is rare, which
is why no one probably has hit it. You have to have a session that is
being dropped by persists. And when the tcp_drop() calls tcp_output.c it
will be in the closed state. The interface must be overloaded and return
ENOBUF's. When that occurs, your flags will be set to
TH_RST (you were dropping the connection). The check in the KASSERT
is trying to make sure you don't have the TH_RST/TH_FIN or TH_SYN
flags in place, but it is the wrong logic it should be != not ==.