mptcp: really cope with fastopen race

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: mptcp: really cope with fastopen race Fastopen and PM-trigger subflow shutdown can race, as reported by syzkaller. In my first attempt to close such race, I missed the fact that the subflow status can change again before the subflow_state_change callback is invoked. Address the issue additionally copying with all the states directly reachable from TCP_FIN_WAIT1.

References

• https://git.kernel.org/stable/c/4bfe217e075d04e63c092df9d40c608e598c2ef2
• https://git.kernel.org/stable/c/e158fb9679d15a2317ec13b4f6301bd26265df2f
• https://git.kernel.org/stable/c/337cebbd850f94147cee05252778f8f78b8c337f