tcp: Apply max RTO to non-TFO SYN+ACK.

tcp: Apply max RTO to non-TFO SYN+ACK.

Since commit 54a378f43425 ("tcp: add the ability to control
max RTO"), TFO SYN+ACK RTO is capped by the TFO full sk's
inet_csk(sk)->icsk_rto_max.

The value is inherited from the parent listener.

Let's apply the same cap to non-TFO SYN+ACK.

Note that req->rsk_listener is always non-NULL when we call
tcp_reqsk_timeout() in reqsk_timer_handler() or tcp_check_req().

It could be NULL for SYN cookie req, but we do not use
req->timeout then.

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20251106003357.273403-6-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>