htx_reserve_max_data() carries an "append_data:" label which is never the target
of a goto: the function simply falls through it. It looks like a leftover from
htx_add_data(), which does use such a label. Let's drop it, the code is reached
by fallthrough anyway and an unused label is only confusing.
if (room < len)
len = room;
-append_data:
htx_change_blk_value_len(htx, tailblk, sz+len);
BUG_ON((int32_t)htx->tail_addr < 0);