MINOR: h3: Set known input payload length of the sedesc

MINOR: h3: Set known input payload length of the sedesc

Set <kip> value when data are transfer to the upper layer, in h3_rcv_buf().
The difference between the known length of the payload before and after a
parsing loop is added to <kip> value. When a content-length is specified in
the message, the h3s <body_len> field is used. Otherwise, it is the h3s
<data_len> field.