total_retrans needs to be cleared in tcp_disconnect().

tcp_disconnect() is rarely used, but it is worth fixing it.

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: SeongJae Park <sjpark@amazon.de>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>