QNetworkAccessManager high CPU usage on arm

QNetworkAccessManager consumes a lot of CPU when doing get or post requests. On raspberry PI2 it consumes 20% CPU when doing simple get/post requests once per second.

It's worth mentioning that the requests are long-polls, in the actuall test long polling timeout was 1 second (resulting in 1 req/sec).

The 5.7.0 version is free of this problem (it consumes 0-1% CPU with the same app).

Also the post() and get() methods take a lot to execute, about 125ms, but this is solvable by running the object in a separate thread. May be this should be a separate bug (because this blocks the event loop and its noticeable in GUI).