QEventDispatcherWin32 on WinCE uses a separate low-priority thread to
monitor sockets activity, so changing the state of notifiers occurs
asynchronously to the main thread. This makes a message-based socket
activation mechanism ineffective.

To avoid timeouts in the helper thread, update the thread's pool
directly from the (un)registerSocketNotifier() functions.

Change-Id: I702c32d69dce09323ca5f65dc2ee1407842e41ef
Reviewed-by: Tobias Koenig <tobias.koenig@kdab.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@theqtcompany.com>