[#1855] Try to calculate the correct amount of written bytes to update the ChannelProgressiveFuture
Introduce a new ChannelOption called DATAGRAM_CHANNEL_ACTIVE_ON_REGISTRATION. Related to [#1830]

This ChannelOption allows to tell the DatagramChannel implementation to be active as soon as they are registrated to their EventLoop. This can be used to make it possible to write to a not bound DatagramChannel.
The ChannelOption is marked as @deprecated as I'm looking for a better solution in master which breaks default behaviour with 4.0 branch.
Correctly handle automatically suspend/resume in ChunkedWriteHandler. Related to [#1861]

The old implementation was broken and could lead to pending message never be picked up again until the user either explicit called flush or
resumeTransfer().
Propagate channelWritabilityChanged() through the pipeline after flushing. Related to [#1861]
Merge remote-tracking branch: upstream/master