usbip: stub-dev synchronize sysfs code paths

Fuzzing uncovered race condition between sysfs code paths in usbip
drivers. Device connect/disconnect code paths initiated through
sysfs interface are prone to races if disconnect happens during
connect and vice versa.

Use sysfs_lock to protect sysfs paths in stub-dev.

Cc: stable@vger.kernel.org
Reported-and-tested-by:  <syzbot+a93fba6d384346a761e3@syzkaller.appspotmail.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Link: https://lore.kernel.org/r/2b182f3561b4a065bf3bf6dce3b0e9944ba17b3f.1616807117.git.skhan@linuxfoundation.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>