[feat] support h264 skip filler data

[kay1ess]

reference T-REC-H.264-201704 7.4.2.7 Filler data RBSP semantics Page(84).
When encoding video by CBR , the real bitrate is low than preset bitrate, which will fill the filler data in h264 bitstream.
For reducing push stream bandwidth, the module support to skip filler data on h264 bitstream when skip_filler_data on;