tcp: partially undo D43792
At the destruction of the tcpcb, no timers are supposed to
be running. However, it turns out that stopping them in the
close() / shutdown() call does not have the desired effect
under all circumstances.
This partially reverts 62d47d73b7eb to reduce the nuisance
caused.
PR:			277009
Reported-by:		syzbot+9a9aa434a14a2b35c3ba@syzkaller.appspotmail.com
Reported-by:		syzbot+e82856782410e895bae7@syzkaller.appspotmail.com
Reviewed By:		glebius, tuexen, transport
Sponsored by:		NetApp, Inc.
Differential Revision:	https://reviews.freebsd.org/D43855