If resultant length of a frame exceeds the maximum value (which is
2**24 - 1 for SPDY/2 and 3), SPDYLAY_ERR_FRAME_TOO_LARGE is used to
indicate this error. This error will be notified by
on_ctrl_not_send_callback.
spdylay_net.h is compatibility layer for network related header files.
In the nature of spdylay library it should not depend on the actual
networking implementations, but we need some system headers for
optimization. Currently, arpha/inet.h and netinet/in.h are needed for
ntoh*/hton* functions.