This function clears the packetbuf and resets all internal state pointers (header size, header pointer, external data pointer). It is used before preparing a packet in the packetbuf or copying a packet to the packetbuf. | This function clears the packetbuf and resets all internal state pointers (header size, header pointer, external data pointer). It is used before preparing a packet in the packetbuf or copying a packet to the packetbuf. |