selftest: packetdrill: Add tcp_fastopen_server_reset-after-disconnect.pkt.

The test reproduces the scenario explained in the previous patch.

Without the patch, the test triggers the warning and cannot see the last
retransmitted packet.

  # ./ksft_runner.sh tcp_fastopen_server_reset-after-disconnect.pkt
  TAP version 13
  1..2
  [   29.229250] ------------[ cut here ]------------
  [   29.231414] WARNING: CPU: 26 PID: 0 at net/ipv4/tcp_timer.c:542 tcp_retransmit_timer+0x32/0x9f0
  ...
  tcp_fastopen_server_reset-after-disconnect.pkt:26: error handling packet: Timed out waiting for packet
  not ok 1 ipv4
  tcp_fastopen_server_reset-after-disconnect.pkt:26: error handling packet: Timed out waiting for packet
  not ok 2 ipv6
  # Totals: pass:0 fail:2 xfail:0 xpass:0 skip:0 error:0

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20250915175800.118793-3-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: q2ven

tools/testing/selftests/net/packetdrill/tcp_fastopen_server_reset-after-disconnect.pkt

@@ -0,0 +1,26 @@
+// SPDX-License-Identifier: GPL-2.0
+`./defaults.sh
+ ./set_sysctls.py /proc/sys/net/ipv4/tcp_fastopen=0x602 /proc/sys/net/ipv4/tcp_timestamps=0`
+
+    0 socket(..., SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
+   +0 bind(3, ..., ...) = 0
+   +0 listen(3, 1) = 0
+
+   +0 < S 0:10(10) win 32792 <mss 1460,nop,nop,sackOK>
+   +0 > S. 0:0(0) ack 11 win 65535 <mss 1460,nop,nop,sackOK>
+
+// sk->sk_state is TCP_SYN_RECV
+  +.1 accept(3, ..., ...) = 4
+
+// tcp_disconnect() sets sk->sk_state to TCP_CLOSE
+   +0 connect(4, AF_UNSPEC, ...) = 0
+   +0 > R. 1:1(0) ack 11 win 65535
+
+// connect() sets sk->sk_state to TCP_SYN_SENT
+   +0 fcntl(4, F_SETFL, O_RDWR|O_NONBLOCK) = 0
+   +0 connect(4, ..., ...) = -1 EINPROGRESS (Operation is now in progress)
+   +0 > S 0:0(0) win 65535 <mss 1460,nop,nop,sackOK,nop,wscale 8>
+
+// tp->fastopen_rsk must be NULL
+   +1 > S 0:0(0) win 65535 <mss 1460,nop,nop,sackOK,nop,wscale 8>