Non-standard USB control requests now handled in own function

Change-Id: Icf56f3f5899d17908dac4783d2b3e30373186eba
Reviewed-on: https://code.wireshark.org/review/3850
Reviewed-by: Michael Mann <mmann78@netscape.net>
Petri-Dish: Michael Mann <mmann78@netscape.net>
Reviewed-by: Anders Broman <a.broman58@gmail.com>