Allow application to call nghttp2_submit_data() in on_frame_send_callback
Allow application to call nghttp2_submit_data() in on_frame_send_callback

Previously we always call on_frame_send_callback before calling
nghttp2_stream_detach_data() after sending DATA frame.  As a result,
even if DATA frame has END_STREAM, application cannot call
nghttp2_submit_data() in on_frame_send_callback because previous data
is still attached.  This commit makes a change so that
nghttp2_stream_detach_data() is called before on_frame_send_callback
so that application can issue nghttp2_submit_data() in the callback.

lukw00/nghttp2,thinred/nghttp2,lukw00/nghttp2,ohyeah521/nghttp2,kelbyludwig/nghttp2,ohyeah521/nghttp2,wzyboy/nghttp2,mixianghang/nghttp2,wzyboy/nghttp2,bxshi/nghttp2,ohyeah521/nghttp2,wzyboy/nghttp2,lukw00/nghttp2,bxshi/nghttp2,minhoryang/nghttp2,shines77/nghttp2,yuki-kodama/nghttp2,dxq-git/nghttp2,lukw00/nghttp2,dxq-git/nghttp2,kelbyludwig/nghttp2,icing/nghttp2,yuki-kodama/nghttp2,serioussam/nghttp2,minhoryang/nghttp2,shines77/nghttp2,mixianghang/nghttp2,ohyeah521/nghttp2,shines77/nghttp2,thinred/nghttp2,thinred/nghttp2,wzyboy/nghttp2,kelbyludwig/nghttp2,thinred/nghttp2,icing/nghttp2,bxshi/nghttp2,serioussam/nghttp2,bxshi/nghttp2,shines77/nghttp2,bxshi/nghttp2,mixianghang/nghttp2,serioussam/nghttp2,ohyeah521/nghttp2,ohyeah521/nghttp2,syohex/nghttp2,dxq-git/nghttp2,icing/nghttp2,kelbyludwig/nghttp2,wzyboy/nghttp2,bxshi/nghttp2,syohex/nghttp2,syohex/nghttp2,serioussam/nghttp2,thinred/nghttp2,syohex/nghttp2,minhoryang/nghttp2,yuki-kodama/nghttp2,lukw00/nghttp2,yuki-kodama/nghttp2,minhoryang/nghttp2,icing/nghttp2,wzyboy/nghttp2,shines77/nghttp2,serioussam/nghttp2,dxq-git/nghttp2,icing/nghttp2,lukw00/nghttp2,yuki-kodama/nghttp2,icing/nghttp2,syohex/nghttp2,minhoryang/nghttp2,mixianghang/nghttp2,mixianghang/nghttp2,syohex/nghttp2,wzyboy/nghttp2,serioussam/nghttp2,kelbyludwig/nghttp2,dxq-git/nghttp2,thinred/nghttp2,thinred/nghttp2,icing/nghttp2,serioussam/nghttp2,minhoryang/nghttp2,yuki-kodama/nghttp2,kelbyludwig/nghttp2,dxq-git/nghttp2,shines77/nghttp2,lukw00/nghttp2,mixianghang/nghttp2