This option is testing the client behavior when it gets response
before sending all request.

Since we do not call on_data_chunk_recv_callback for ignored DATA
chunk, if nghttp2_option_set_no_auto_connection_window_update is used,
application may not have a chance to send connection WINDOW_UPDATE.
To fix this, we accumulate those received bytes, and if it exceeds
certain number, we automatically send connection-level WINDOW_UPDATE.

This commits changes the upper bound of one header field size (the sum
of the length of name and value) to 64KiB by default.  We may add an
option to change this upper bound in the future.

For now, if request has request body, we'll issue RST_STREAM to inform
the peer to stop sending body.  RST_STREAM may be sent before error
page header or data, so peer may receive RST_STREAM only.

The number of failed stream is counted multiple times if several
connection attempts are made.