linsysfs(4): Keep Linux compatible sysfs the same as Ubuntu

By checking Ubuntu, there is no `/sys/subsystem' in sysfs. To compatible
with Ubuntu, delete the 'subsystem' creation in Linux compatible module.

On the other hand, the sysfs `/sys/subsystem' cause failure for some
Linux udev cases. In Linux udev source code, there is a function named
scan_devices_all', and it will scan /sys/subsystem' if it is existed,
but now there are nothing in /sys/subsystem `, and it returns empty
to cause some use cases failed.

Reviewed by: dchagin
Differential Revision: https://reviews.freebsd.org/D38885
MFC after: 1 month
XMFC with: ifAPI