avformat/hlsenc: copy codec_tag when stream copy

avformat/hlsenc: copy codec_tag when stream copy

when use fmp4 segment type in hls and use codec copy,
there have an error message.
error message:
   [mp4 @ 0x25df020] Tag avc1 incompatible with output codec id '28' ([33][0][0][0])
   [hls @ 0x2615c80] Some of the provided format options in '(null)' are not recognized
   Could not write header for output file #0 (incorrect codec parameters ?): Invalid argument
this patch can fix it.

Signed-off-by: Liu Qi <w_liuqi@kingsoft.com>
Signed-off-by: Steven Liu <lq@onvideo.cn>