Merge branch 'tcp-provide-better-locality-for-retransmit-timer'

Eric Dumazet says:

====================
tcp: provide better locality for retransmit timer

TCP stack uses three timers per flow, currently spread this way:

- sk->sk_timer : keepalive timer
- icsk->icsk_retransmit_timer : retransmit timer
- icsk->icsk_delack_timer : delayed ack timer

This series moves the retransmit timer to sk->sk_timer location,
to increase data locality in TX paths.

keepalive timers are not often used, this change should be neutral for them.

After the series we have following fields:

- sk->tcp_retransmit_timer : retransmit timer, in sock_write_tx group
- icsk->icsk_delack_timer : delayed ack timer
- icsk->icsk_keepalive_timer : keepalive timer

Moving icsk_delack_timer in a beter location would also be welcomed.
====================

Link: https://patch.msgid.link/20251124175013.1473655-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>