Don't try to adjust a TLS TOE socket that has been closed.

The handshake timer can race with another thread sending a FIN or RST
to close a TOE TLS socket. Just bail from the timer without
rescheduling if the connection is closed when the timer fires.

Reported by: Sony Arpita Das @ Chelsio QA
Reviewed by: np
Differential Revision: https://reviews.freebsd.org/D27583