* do endian conversion in usbredirparser where necessary

  * update serialize format (comment only) to be little endian, and also do

    endian conversion there so be -> le and visa versa serialisation becomes

    possible

* check length against max packet size

* check caps for relevant callbacks in parser

* cancel pending packets / active streams before reset?

* add a queue_buf call to parser, use it in host to avoid memcpy of

  "in" bulk transfers