Fix for tcp_shutdown test // assertion in usock_win.inc

How to reproduce
<pre>
cmake <path to nanomsg>  -G"Visual Studio 11 Win64"
cmake --build . --config Debug
ctest -VV -C Debug
...
test 6
      Start  6: tcp_shutdown

6: Test command: C:\WORK\GITHUB\messaging\dev\build\Debug\tcp_shutdown.exe
6: Test timeout computed to be: 9.99988e+006
6: Assertion failed: 8 == NN_USOCK_STATE_ACTIVE (c:\work\github\messaging\dev\nanomsg\src\aio\usock_win.inc:326)
 6/29 Test  #6: tcp_shutdown .....................***Failed    3.42 sec
...
97% tests passed, 1 tests failed out of 29

Total Test time (real) =   9.76 sec

The following tests FAILED:
          6 - tcp_shutdown (Failed)
Errors while running CTest
</pre>

I've combined solution by @tailhook from #172 and  by @norsd from #211 
It will fix the issue with shutdown.