linux_usbfs: Add support for kernels that can reap after disconnect

linux_usbfs: Add support for kernels that can reap after disconnect

For kernels that support the REAP_AFTER_DISCONNECT capability, it is
no longer necessary to use the nasty workaround that is the
usbi_handle_disconnect() function. All transfers can be properly
reaped as one would expect and will have an appropriate URB status.

Note that moving usbi_handle_disconnect() after the hotplug section
is fine because the hotplug disconnect message simply gets added to
the hotplug_msgs list to be processed the next time handle_events()
is called.

Signed-off-by: Chris Dickens <christopher.a.dickens@gmail.com>