tcp: reduce tcp_comp_sack_slack_ns default value to 10 usec

tcp: reduce tcp_comp_sack_slack_ns default value to 10 usec

net.ipv4.tcp_comp_sack_slack_ns current default value is too high.

When a flow has many drops (1 % or more), and small RTT, adding 100 usec
before sending SACK stalls the sender relying on getting SACK
fast enough to keep the pipe busy.

Decrease the default to 10 usec.

This is orthogonal to Congestion Control heuristics to determine
if drops are caused by congestion or not.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Neal Cardwell <ncardwell@google.com>
Link: https://patch.msgid.link/20251114135141.3810964-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>