Control video packets send rate (thanks Faba Aa for the feedback)

[nanang]

As described ​here:

When generate a keyframe, vid_stream will try to send out the data
as soon as possible, the peak bandwidth may over ADSL's capability
even if the average video bps is suitable for ADSL. Under this
situation, ISP will drop data. I think we need to control send rate
to avoid this.

[nanang]

(In [4043]) Re #1476: Initial version of send rate control in video stream, added simple blocking method (block application thread to make send delay when delay is needed).

[bennylp]

(In [4059]) Re #1476: for simple blocking, the bandwidth typically needs to be set to larger value than the avg_bitrage, otherwise the simple_blocking will slow down the transmission too much, causing video and audio unsync. This patch force the bandwidth to at least three times avg_bps