If the data in a linked list of accessors is less than min_len (the second parameter), bf_packIffLess(pack, min_len) packs the data by calling bf_pack().
bf_packIffLess() is often called to ensure that a packet's header is in a single contiguous buffer so that the individual fields of the header can be easily accessed.
For a detailed description of the network service's buffer management, click here.