UPSTREAM: tcp: start receiver buffer autotuning sooner

Previously receiver buffer auto-tuning starts after receiving
one advertised window amount of data. After the initial receiver
buffer was raised by patch a337531b942b ("tcp: up initial rmem to
128KB and SYN rwin to around 64KB"), the reciver buffer may take
too long to start raising. To address this issue, this patch lowers
the initial bytes expected to receive roughly the expected sender's
initial window.

Fixes: a337531b942b ("tcp: up initial rmem to 128KB and SYN rwin to around 64KB")
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Wei Wang <weiwan@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 041a14d2671573611ffd6412bc16e2f64469f7fb)
Signed-off-by: Chenbo Feng <fengc@google.com>

This patch is backported from 4.20 to allow us to drop "ANDROID: net:
ipv4: tcp: add a sysctl to config the tcp_default_init_rwnd"

Bug: 118591209
Test: net_test sock_diag_test.py
Change-Id: Ifff58b0b86a816a66d5a0bd77b57d6eedeaafa3b