WinRT: Only set keepalive socket option in certain socket states

The keepalive socket can only be set if the socket is not connected
(see
http://msdn.microsoft.com/en-us/library/ie/windows.networking.sockets.streamsocketcontrol.keepalive)

Task-number: QTBUG-38623
Change-Id: Ia40dc66f071a8109538e4be7a8f420de81d5be8d
Reviewed-by: Alex Trotsenko <alex1973tr@gmail.com>
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@theqtcompany.com>
Reviewed-by: Andrew Knight <andrew.knight@theqtcompany.com>

src/network/socket/qabstractsocket.cpp

@@ -1882,6 +1882,9 @@ bool QAbstractSocket::setSocketDescriptor(qintptr socketDescriptor, SocketState
     \since 4.6
     Sets the given \a option to the value described by \a value.
 
+    \note On Windows Runtime, QAbstractSocket::KeepAliveOption must be set
+    before the socket is connected.
+
     \sa socketOption()
 */
 void QAbstractSocket::setSocketOption(QAbstractSocket::SocketOption option, const QVariant &value)

src/network/socket/qnativesocketengine_winrt.cpp

@@ -998,7 +998,8 @@ bool QNativeSocketEnginePrivate::setOption(QAbstractSocketEngine::SocketOption o
         return true;
     }
     case QAbstractSocketEngine::KeepAliveOption: {
-        if (socketType == QAbstractSocket::UdpSocket)
+        if (socketType == QAbstractSocket::UdpSocket
+                || socketState != QAbstractSocket::UnconnectedState)
             return false;
 
         boolean keepAlive = v;