tcp: Add new args for cong_control in tcp_congestion_ops

This patch adds two new arguments for cong_control of struct
tcp_congestion_ops:
 - ack
 - flag
These two arguments are inherited from the caller tcp_cong_control in
tcp_intput.c. One use case of them is to update cwnd and pacing rate
inside cong_control based on the info they provide. For example, the
flag can be used to decide if it is the right time to raise or reduce a
sender's cwnd.

Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Miao Xu <miaxu@meta.com>
Link: https://lore.kernel.org/r/20240502042318.801932-2-miaxu@meta.com


Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>