tcp: drop data received after a FIN has been processed

RFC 9293 describes the handling of data in the CLOSE-WAIT, CLOSING,
LAST-ACK, and TIME-WAIT states:
This should not occur since a FIN has been received from the remote
side. Ignore the segment text.
Therefore, implement this handling.

Reviewed by: rrs, rscheff
Sponsored by: Netflix, Inc.
Differential Revision: https://reviews.freebsd.org/D44746

(cherry picked from commit c9cd686bd4a039c652ed5d11019bae10828329df)