BlackBerry: Prevent superfluous removal of socket notifiers

File descriptors have always been removed from bps before adding them,
which lead to an annoying warning.
"QEventDispatcherUNIX::registerSocketNotifier()" needs to be called
after "ioEvents()" to prevent this.

Back-port of qtbase/e9c51a1fdc9092e5589fd6f823ad0e704e293c88

Task-number: QTBUG-34536

Change-Id: I767a15cb2883bc820da5c858613ffb26abc002e4
Reviewed-by: Thomas McGuire <thomas.mcguire@kdab.com>
Reviewed-by: Petr Nejedlý <pnejedly@blackberry.com>