Merge branch 'Fix-reconnection-latency-caused-by-FIN-ACK-handling-race'

SeongJae Park says:

====================
Fix reconnection latency caused by FIN/ACK handling race

The first patch fixes the problem by adjusting the first resend delay of
the SYN in the case.  The second one adds a user space test to reproduce
this problem.

From v2
(https://lore.kernel.org/linux-kselftest/20200201071859.4231-1-sj38.park@gmail.com/)
 - Use TCP_TIMEOUT_MIN as reduced delay (Neal Cardwall)
 - Add Reviewed-by and Signed-off-by from Eric Dumazet

From v1
(https://lore.kernel.org/linux-kselftest/20200131122421.23286-1-sjpark@amazon.com/

)
 - Drop the trivial comment fix patch (Eric Dumazet)
 - Limit the delay adjustment to only the first SYN resend (Eric Dumazet)
 - selftest: Avoid use of hard-coded port number (Eric Dumazet)
 - Explain RST/ACK and FIN/ACK has no big difference (Neal Cardwell)
====================

Signed-off-by: Jakub Kicinski <kuba@kernel.org>