staging: usbip: bugfix prevent driver unbind

Implemented pre_reset and post_reset methods of the driver to prevent the
driver from being unbound upon a device reset. Because of this also the
asynchronous reset introduced to prevent a race condition is no longer necessary
(and sometimes causes problems, because it comes later then expected).

Signed-off-by: Arjan Mels <arjan.mels@gmx.net>
Cc: Greg Kroah-Hartman <gregkh@suse.de>
Cc: Takahiro Hirofuchi <hirofuchi@users.sourceforge.net>
Cc: Max Vozeler <max@vozeler.com>
Cc: usbip-devel <usbip-devel@lists.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>