usbip: usbip_host: run rebind from exit when module is removed

After removing usbip_host module, devices it releases are left without
a driver. For example, when a keyboard or a mass storage device are
bound to usbip_host when it is removed, these devices are no longer
bound to any driver.

Fix it to run device_attach() from the module exit routine to restore
the devices to their original drivers. This includes cleanup changes
and moving device_attach() code to a common routine to be called from
rebind_store() and usbip_host_exit().

Signed-off-by: Shuah Khan (Samsung OSG) <shuah@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>