Race: Thread::interrupt vs. AbstractInterruptibleChannel.begin

There is a race interrupting a thread B that begins a blocking NIO operation, e.g. socket accept.

Thread A.........................Thread B

                                 enters ServerSocketChannelImpl::accept
                                   enters AbstractInterruptibleChannel::begin
enters B.interrupt
    reads B.nioBlocker -> null
                                        writes B.nioBlocker = AbstractInterruptibleChannel.interruptor
                                        reads B.interrupted -> false
    writes B.interrupted = true
                                   leaves AbstractInterruptibleChannel::begin
                                   [...]
                                       enters Net.accept

Result: B successfully calls accept and remains there even though it was interrupted.

How to reproduce:

- apply decide_race_in_thread_interrupt.patch (attached)

- run ThreadInterruptRace.java (also attached) like this
  java ThreadInterruptRace.java dosleep

The issue was found analyzing failures of jck test api/java_net/ServerSocket/AcceptInterruptibleTests_PlatformThreads

Potential fix: write `interrupted` field before reading `nioBlocker` in Thread::interrupt