refactor deny_new_usb syctl into usb core sysctl table registration #50
Description
It's discouraged to define sysctls in kernel/sysctl.c but as the usb subsystem can be totally isolated into a kernel module, there are no appropriate places to put it in a clean way. It would be better to register a sysctl table in the usb core and use deny_new_usb there, which will work no matter if usb is compiled in or used as a module.