Fix for first issue from #1652 on computation of time to wait in AbstractTrafficShapingHandler for Netty 4

Fix for first issue from #1652 on computation of time to wait in AbstractTrafficShapingHandler for Netty 4, using the same formula than in Netty 3 (wrong place for parenthese).
Was:

    (bytes * 1000 / limit - interval / 10) * 10;

Becomes:

    (bytes * 1000 / limit - interval) / 10 * 10;