nghttpx: Fix connection preface is not read by upstream_http2_connhd_readcb
nghttpx: Fix connection preface is not read by upstream_http2_connhd_readcb

It seems that if readcb is not set before SSL/TLS handshake, the
incoming data already available when eventcb (BEV_EVENT_CONNECTED
event) is fired is not further notified after setting new readcb.  We
knew this fact and call upstream->on_read() in eventcb, but it is
wrong for HTTP/2.  We have to call upstream_http2_connhd_readcb to
check connection preface.  Otherwise, we consume it by nghttp2 session
and it is treated as unknown frame and connection preface is not
detected properly.

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